CA2049133C - Methods and apparatus for implementing data bases to provide object-oriented invocation of applications - Google Patents

Abstract

The data bases include method entries, message entries, and class entries. Method entries refer to commands or other mechanisms used to invoke applications. Message entries each represent a type of operation which can be performed on instances in a class which correspond to that message and identify a method map which contains one or more references to method entries stored in the data base. Class entries, each of which is unique in a data base, and identify types of instances having common characteristics as well as identifying a corresponding group of message entries. The data bases may be in a data processing network comprised of one or more platforms or nodes and may be either global data bases accessible to the entire network or local data bases, each of which is accessible to only a part of the network.

Description

2û ~9 ~ ~ 3 I. RELATED APPLICATIONS
This application is related to Canadian serial number 2,049,121 entitled "METHODS AND APPARATUS FOR PROVIDING
DYNAMIC INVOCATION OF APPLICATIONS IN A DISTRIBUTED
S HETEROGENEOUS ENVIRONMENT", Canadian serial number 2,049,143 entitled "METHODS AND APPARATUS FOR PROVIDING A
CLIENT INTERFACE TO AN OBJECT-ORIENTED INVOCATION OF AN
APPLICATION", and Canadian serial number 2,049,125 entitled "METHODS AND APPARATUS FOR IMPLEMENTING S~K FUNCTIONS IN
A DISTRIBUTED HETEROGENEOUS ENVIRONMENT", all filed the same day as this application.

II. BACKGROUND OF THE INVENTION
This invention relates to the interaction of computer applications across a heterogeneous data processing network. Specifically, this invention relates to the organization of a data processing network in accordance with an object-oriented model and the interaction of independent applications across such a heterogeneous network environment.
Computers commlln;cate with each other over data processing networks. The computers themselves are referred generally as "nodesr', and a specific type of computer, that is a specific type of hardware using a specific type of operating system, is referred to as a "platform". Networks containing different types of platforms are called "heterogeneous networks". One purpose for connecting platforms in a network is to provide different environments in which to execute application programs (referred to as "applications" for brevity on shared data.

~L

In the typical data processing network, different platforms and application~ rl~nn~ng on different platforms store information in their own specific manner. For example, in a VAX.VMS platform, text editing tasks may be accomplished using a TPU text editor, while in a MIPS.ULTRIX platform, text editing tasks may be accomplished using an EMACS text editor.
Users of a network having both platforms may wish to use operations from the different text editors on the different platforms without having to know the details of those platforms and text editor~.
This compatibility has not previously been possible.
Instead, conventional networks require users of a heterogeneous network to employ the specific interface each application requires for operations on specific platforms.
Conventional network~ fail to provide users with a capability to communicate between applications using a standard inter~ace.
As an example of the difficulties of interapplication communication on a conventional heterogeneous network, suppose that the user of a text editor application on one platform desired to access a multi-user data base retrieval service, such a~ DIALOG for scientific articles or LEXIS for court opinions, on another platform. To do 80 on a conventional network, the text editor appliaation's operation would have to be suspended, and the data base retrieval service would have to be invoked using commands and messages specific to the data base retrieval service. The user would not only need to know the specific names of each service i de~ired, but would also have to know the location of the service in the network and would have to be familiar with the different commands and command formats employed by each service.
As yet no standard interface has been developed to allow an application in one platform to invoke an application on a different platform in a heterogeneous network in an efficient and uncomplicated manner. Instead, conventional lnterapplication communication merely provide~ mechanism~ for phy~ically tran~porting messages and data between applications.
One example of a mechanism which is presently u~ed to allow an application on one platform to communicate with an application on a different platform i~ a Remote Procedure Call (RPC) system. An RPC system on one platform re~pond~ to queries from an "invoking~ application by first translating that application's messages into a network data format, and then transmitting the translated queries over the network to a receiving platform. At the receiving platform, another component of the RPC sy~tem decodes translated messages into queries in a data format acceptable to the application invoked. The original mes~ages from the invoking platform, however, need to be consi~tent with a syntax dictated by the invoked application.
Another difficulty with conventional networks occurs when the application on a remote node is not currently loaded and rllnn~ ng . Many RPC ~ystems only allow remote invocation of applications that are already loadèd and running. If this is not the case, the user of the client applications must find some way to load the server application on the remote platform before invoking it. This can be severely limiting.
One obstacle to implementing a network-wide system to facilitate interapplication communication has been the large amount of system resources which had been thought to be required of a system in order to handle all the different types of data, operations and applicatlons in a network. As a network expands, the systems, resources, and re~uirements would increase as well, making many proposed implementation~
completely unwieldy.
There is, therefore, a need for an efficient and simple manner for applications on different platforms to communicate with each other, such as through a uniform and consistent interface for applications. There iB also a need for a dynamic invocation environment for applications in a distributed heterogeneous environment.
III. SUMMARY OF THE lNv~NLION
To achieve these needs, the present invention provides for interaction of processes in an object-oriented manner by which a system manages "classes" of data instances and applications rather than managing the data itself. The management of such classes involves a data base which contains information about the classes, such as certain common attributes of applications or instances which are supported by the classes.
Client applications can remotely invoke other applications by se~ng globally (i.e., network-wide) , recognized me~age~ with parameter~. UQing the mes~age names, as well a~ information about the cla~ses of certain parameter~, a reference to a specific method i8 selected from the data baQe. That method will perform the operation ~pecified in the me~age. Other 2 0 ~ ~ ~ 3 3 ~ . ~
lnformation in the data base is then used to locate and execute the actual code to implement the referenced method.
According to one aspect, the present invention provides in a data processing network which includes: a plurality of applications capable of performing operations on instances and capable of sending and receiving messages including identifiers for instance and types of operations; a plurality of instances corresponding to each of said applications, and a plurality of platforms operating under the control of operating systems for executing said applications;
a system for organizing communlcation among said applications in an ob~ect-oriented manner comprising: memory in the network containlng a data base, said data base including: a plurality of method entries, each of said method entries corresponding to one of said applications and containing a reference to a means external to the data base for invoking a procedure to allow that application to perform a specified operation on a specified instance, a plurality of non-redundant class entries, each of said class entries containing information about a class consisting of one or more instances which share common characteristics and further containing an identification on one or more message entries, and a plurality of message entries, each of said message entries specifying information about the types of operations which may be performed on selected instances and further containing a reference to one or more method entries, the message entries identified in each class entry containing information about the types of operations which can be performed on instances 9 ~ -~ 3 associated with said class entry, and the method entries identified ln each message entry contalnlng lnformatlon relatlng to appllcatlons capable of performlng the types of operatlons speclfied ln said message entry; database control means coupled to the memory in the network, includlng: means, responsive to a message from a client application, for selecting the class entries and message entrles associated wlth the lnstance and type of operation identifled in sald message, means for selecting a method entry referenced ln the selected message entry and corresponding to the requested application, means for selecting a platform capable of executing the requested application, and means for transmitting the identifier for the instance and the reference to a procedure contained in the selected platform; and, an object definition facility coupled to the memory in the network, wherein the data base includes a global class portion which is accessible throughout the network and local portions which are each accessible to only a portion of the network, wherein the data base control means includes means for searching the local data bases in a predetermined order before searching the global class data base, and wherein the obiect definition facility includes means for generating globally unique identifiers for types of operations and instances.
According to another aspect, the present invention provides in a data processing network which includes: a plurality of applications capable of performing operations on instances and capable of sending and receiving messages including identifiers for instance and types of operations; a - 5a - .

... ~ .

-~ ~ ~ 9 ~ 3 3 plurality of instances corresponding to each of said applications, and a plurality of platforms operating under the control of operating systems for executing said applications;
a system for organizing communication among said applications in an ob~ect-oriented manner; and memory in the network containing a data base; a method of modifying the data base, said method comprising the steps of: making a plurality of method entries, each of said method entr~es corresponding to one of said applications and containing a reference to a means external to the data base for invoking a procedure to allow that application to perform a specified operation on a specified instance, making a plurality of non-redundant class entries, each of said class entries containing information about a class consisting of one or more instances which share common characteristics and further containing an identification on one or more message entries, and making a plurality of message entries, each of sald message entries specifying information about the types of operations which may be performed on selected instances and further containing a reference to one or more method entries, the message entries identified in each class entry containing information about the types of operations which can be performed on instances associated with said class entry, and the method entries identified in each message entry containing information relating to applications capable of performing the types of operations specified in said message entry; controlling by data base control means coupled to the memory in the network, said controlling including the steps of: selecting, responsive - 5b -~ 0 ~ $ ~ ~ ~
to a message from a cllent application, the class entries and message entrles associated with the instance and type of operation identified in said message, selecting a method entry referenced in the selected message entry and corresponding to the requested application, means for selecting a platform capable of executing the requested application, and transmitting the identifier for the instance and the reference to a procedure contained in the selected platform; and, coupling an obiect definition facility to the memory in the network, wherein the data base includes a global class portion which is accessible throughout the network and local portions which are each accessible to only a portion of the network, wherein the data base control means includes means for searching the local data bases in a predetermined order before searching the global class data base, and wherein the object definition facility includes means for generating globally unique identifiers for types of operations and instances.
More partlcularly, ln a memory resldent ln a data processing network which allows remote invocation of applications, a class data base for use in the data processing network comprises method entries each containing a reference to a corresponding invocation command to invoke one of the applications; message entries containing information for a plurality of messages, each of the messages specifying the types of operations which can be performed on instances ln the correspondlng ones of a plurallty of classes, each of the message entries containing an identification of a correspondlng group of the method entrles; and a plurallty of - 5c -.~

~ 9 ~ ~ ~
class entries each containing information for a different, uniquely-identifiable class, the classes identifying types of the instances, which are items that may be manipulated or accessed by the applications, according to shared characteristics, each of the class entries containing an identification of a corresponding group of the message entries.
A process of modlfying the class data base for a new application, ln accordance with this invention, operates in a data processing network having a class data base for use in allowing remote invocation of applications. The class data base is resident in memory in the data processing network and includes a plurality of class entries containing lnformation for a plurality of uniquely-identifiable classes, the classes identlfying types of the instances, which are items that may be manipulated or accessed by the applications, according to shared - 5d -A

., characteristics. Each of the class entries contains an ~dentification of a correspo~;ng group of message entrie~, and the message entries contain information for a plurality of messages, each of the messages specifying the types of operations which can be performed on instances in the cOrre8pO~ ng classes. Each of the message entries contains an identification of a correspon~;ng group of method entries containing references to invocation commands to invoke the applications. The application contains a plurality of messages, and the process comprises the step~, performed by the data processing network, of f; n~; ng, for each of the messages for the new application, the correspo~; ng class entry ~; ng to each corresponding class entry a message entry containing an identification of the correspo~ng message: and adding to each message entry identifications for method entries for the message correspo~ ng to the message entry.
The accompanying drawinge which are incorporated in and which constitute part of this specification, illustrate an implementation of the invention and, together with the description, explain the principles of the invention.
IV. BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a diagram of a network which can be used in a preferred implementation of the present invention.
Figure 2 is an illustration of the ma~or components of an object-oriented model of this invention in relationship to an application.
Figure 3 is an illustration of the relationships between the components of the object-oriented model of this implementation of the present invention.
Figure 4 is an illu~tration of the relationships between examples of the components of the ob;ect-oriented model of this invention.
Figure 5 is an illustration of a structure for a class data base according to the preferred implementation and consistent with the relationships illustrated in Figure 4.
Figure 6 is a diagram of the different components of the preferred implementation, and of the preferred flow of information between these components.
Figure 7 i8 a diagram showing the relationships of the different memory ~ystems in the preferred implementation.
Figure 8 i8 a diagram of a preferred structure of a local class data base.
Figure 9 is a diagram of a preferred implementation of a block in the local class data base shown in Figure 8.
Figure 10 is an illustration of the function of a loader/unloader for a global data base, a local data base, and a node cache.
Figure llA iB a diagram illustrating à preferred implementation of a context object data base.
Figure llB is a diagram illustrating a preferred implementatioh of a method override table in the context ob~ect data base shown in Figure llA.

4~

Figure llC is a diagram illustrating a preferred storage structure for a server node table in the context object data base shown in Figure llA.
Figure llD is a diagram illustrating a preferred implementation of a class data base override table in the context object data base shown in Figure llA.
Figure 12 is a diagram of individual software components in the platforms of the network.
Figure 13 is a flow diagram of the general operation performed b~ the preferred implementation of this invention for remote invocation of applications.
Figure 14 is a more detailed diagram of components of the network and the flow of information.
Figures 15A through 15D are a flow diagram of the procedure performed by the invoker software component in Figure 14.
Figure 16 is an illustration of the steps performed by the invoker software component in Figure 14 to resolve a method.
Figures 17A and 17B are a flow diagram of the steps performed by the control server software component in Figure 14.
Figures 18A and 18B are a flow diagram of the steps performed by the dispatcher software component in Figure 14.
V. DETAILED DESCRIPTION OF THE PREFERRED IMPLEMENTATION
Reference will now be made in detail to preferred implementations of the invention as illustrated in the accompany-ing drawings.
This invention is preferably implemented by data processors organized in a conventional network architecture. The architecture for and procedures to implement application interoperability, however, are not conventional, as they provide for an object-oriented approach to the interactions between appl~cation~ in the network.
A. The Ma~or ComPonents of the Network Figure l illustrates a network 50 which can be used to implement the present invention. In Figure 1, network 50 contains three independent platforms 100, 200, and 300 which are connected by a network bus 55. Although platforms 100, 200, and 300 are shown as completely heterogeneous (i.e., platform 100 is shown a~ a VAX processor using a VMS operating system, platform 200 is shown as a MIPS processor using an ULTRIX operating system, and platform 300 is shown as an 80286 processor using a MS-DOS operating system), this invention will operate in a homogeneous network as well. Also, the number of platforms is not important.
The composition and protocol of the network bus 55 is not important as long as it allows for c~ ~n~ cation of the information between platforms 100, 200, and 300. In addition, the specific network architecture is not crucial to this invention. For example, another network architecture that could be used in accordance with this invention would employ one platform as a network controller to which all the other platforms would be connected. It i8 believed, however, that the network 50 shown in Figure 1 enhances the advantages of the present invention.
In the preferred implementation of network 50, platforms 100, 200, and 300 each include a central processing CA 02049l33 l998-04-09 unit ("CPU") 110, 210, and 310 respectively, and a memory, 150, 250, 350, respectively.
Included within each central proce~sing unit 110, 210, and 310, are applications 120, 220, and 320, respectively, operating systems ("OP SYS") 140, 240, and 340, respectively, and the Application Control Architecture Services ("ACAS") software components 130, 230, and 330, respectively.
Applications 120, 220, and 320 can be programs that are either previously written and modified to work with the present invention, or that are specially written to take advantage of the services offered by the pre8ent invention.
For purpose~ of this description, applications either invoke operations to be performed in accordance with this invention, or respond to the invocation by other applications.
ACAS software components, 130, 230, and 330 implement the object-oriented approach of this invention.
Preferably, ACAS software components 130, 230, and 330 consist of a number of software modules as described in greater detail below.
Operating 8y8tem8 140, 240, ànd 340 are the 8t~n~rd operating systems which are tied to the correspo~ ng CPUs 110, 210, and 310, respectively, of the platform 100, 200, and 300, re~pectively.
Memories 150, 250, and 350 serve se~eral functions.
One of the functions is, of course, to provide general storage for the associated platform. Another function is to store application8 120, 220, and 320, ACAS software components 130, 230, and 330, and operating systems 140, 240, and 340 prior to their execution by the respective CPU 110, 310, and 310.
In addition, portions of memories 150, 250, and 350 contain information for a network wide, or "global," data base which is shared and available directly or indirectly by all of the platforms 100, 200, and 300 in network 50. The global data base is described in greater detail below.
B. Elements of the Ob~ect-Oriented Architecture (1) Definitions of the Elements Ob;ect-oriented methods have been used in programming to separate the interface of data from actual implementation, but such methods have not been applied to heterogeneous networks. In the present invention, ob;ect-oriented techniques are used to separate the actual applications and their data from the implementation of operations on that data by other applications.
The object-oriented architecture of this invention preferably includes certain key elements. Figure 2 explains the relationship between certain of those elements and certain conventional features of applications. As shown in Figure 2, an application 260 can be described in two ways. First, that application has certain application definitions 265. For example, if the application 260 is a word processing program, then the application definitions could include definitions of what operations that word processing program can perform and what kind of data that word processing system can operate upon.
In addition, application 260 includes application , ,~. 1 . .

data 268. Application data 268 is the specific data upon which application 260 operates.
In accordance with the present invention, the application data is not "handled" by the object-oriented architecture. Instead, the present invention is organized around characterizing the application definitions and the application data in term~ of object types, as referred to in the remainder of this description as objects. Objects are not shown in Figure 2, but they pervade the elements that are shown.
In the discussion which follows, the term "object"
will refer generally to several different kinds of elements, all of which have two characteristics in common. First, they refer to external capabilities, me~n;ng that objects refer to or describe those portions of application definitions or application data which need to be communicated with other applications. Second, they are generic me~n;ng that objects are intended to be available to all applications, and as such have a universally recognized and unique name for all applications that have interfaces to the objects. The present invention involves the handling of objects rather than the handling of specific data or applications.
As shown in Figure 2, two elements of the ob;ect-oriented architecture of this invention are developed from the application definitions 265. One is classes 270 and the other iB methods 280. Classes are objects in the sense that the names of the classes and the features of the classes are both external and generic. Furthermore, classes can be used as means for descrlbing not only applications, but also the data used by the applications.
In addition, one can derive certain types of operations from the application definitions 265 that are performed by that application, and these are specific examples of methods 280. Again, however, the specific methods 280 are not managed by the system, but rather can be organized into classes. The classes for those methods (called method objects) are generic and external, even though the specific commands or operations executed by the applications are not.
Instances 290, which are derived from the application data 268, are items that may be manipulated or accessed by an application. Again, the instances are not objects managed by this architecture. Instead, instances are organized into classes such that instances in the same classes share common characteristics. For example, a specific DECwrite application, which is a compound document editor, may be operating on a specific file called MYFILE. This is a specific file, and it is not handled by the ACAS system.
Instead, MYFILE may belong to a class of compatible files, such as ASCII_FILE, which is generic and therefore a class object.
By the same token, a specific DECwrite appliaation is not managed by the entire system. Instead, however, the ~pecific DECwrite application may belong to a class called DECwrite whiah is generic and a class object.
As can be seen from Figure 2, applications can then be characterized by the classes to which the applications ... . . . . . .. ~ .

belong, by the classes (method objects) which support the specific methods in that application, and by the clas~ objects upon which the method objects can operate.
One of the feature~ of clas~es is that they may be hierarchically organized. This is explained in greater detail below, but may be understood prel~m~nArily by considering the concept of superclasses and subclasses. A superclass is a parent o~ its subcla~ses, and each subclass is a child of at least one superclass. The superclass/subclass relationship means that the attributes or shared characteristics of the superclass are inherited by the subclass. For example, a class of DATA FILES may have as attributes the capability of being opened, read, and written. Two subclasses of the cla~s DATA_FILES could be of SEQUENTIA~_FILES and RANDOM-ACCESS-FILES. In addition to the attributes of being able to be opened, read, and written, the subclass SEQUENTIAL_FILES could al80 have the attribute of being acce~sible sequentially, and the subclas~ RANDOM_ACCESS_FILES could have the attribute of being acces~ible directly by an address.
Another element of the ob~ect-oriented architecture of this invention not reflected in Figure 2 is messages.
Messages are the interfaces between an application program and the methods, and are used in the application program to specify types of operations which can be performed on the instances identified in the client application. The message~
are generally in the form of a selector of an operation, such as PRINT, and several parameters, which can be instance~, strings, numbers, etc. The relationship between these elements is described in the next section.
(2) RelationshiP of Elements Figure 3 is a diagram showing the relation8hip of the different elements previously described. As Figure 3 demonstrates, each instance 370 is associated with a cla8s 380. Another way of understanding this is to consider class 380 as a "template" for the creation of objects in that class, which can be instances, as well as for the manipulation of such objects. The term "template" denotes the fact that the objects (be they data items, methods, or applications) in each class, share certain characteristics or attributes determined by that class.
An instance 370 is manipulated by senA~n~ a message 360. The message 360 might be an action, such as EDIT, READ
or PRINT. Mes8ages are said to be "supported" by the class, which means that the interpretation of the message depends upon the classes to which the instances in that message belong. For example, a PRINT message may be interpreted differently if the instance is a text file in the class TEXT_FI~E, as opposed to a color graphic8 file in a clas~
COLOR_GRAPHICS.
A message 360 does not describe the implementation of a particular operation; it only represents the interface to the implementation of a particular operation. Thus, to find the particular operation that is called for by a particular message 360 (i.e., the method), one must not only examine the message, but also the class of the instance. To cause a specific action to occur, the message 360 must be mapped to -actual executable program code. This mapping occurs by f~n~ing the particular message 360 which corresponds to the partlcular cla~s 380 of the particular instance 370 and then finding the particular method 390 which corresponds to the message 360 supported by the class 380. The method 390 represents the actual executable program code to implement the desired operation of the message 360 on the instance 370.

(3) Orqanization Figure 4 shows a representation of how the different object-oriented architecture elements can be organized preparatory to their specific representation in memory. As is apparent from Figure 4, there is a complex relation~hip involved between the classes and the methods. A hierarchy is used for both methods and classes in the preferred implementation to effect the ob~ect-oriented approach necessary to reflect the behavioral relationship~ which must exist among the applications. The specific examples given, however, are merely illustrative, and other types of representations for these classes and methods may be apparent to those skilled in the art.
In the diagrammatic repre8entation shown in Figure 4, there are essentially two branches of the hierarchy. One is headed by method object 400 and the other by class 450.
The branches, hierarchies differ by what is inherited. In the class hierarchy, the inheritance is of behaviour because such inheritance includes messages. In the method hierarchy the inheritance is only of attributes. The bridge between the class hierarchy and the method hierarchy is by way of the messages, such a~ messages 490 and 495, and the method map8, such a8 maps 493 and 498. In the method hierarchy shown in Figure 4, method objects, 410, 415, and 420, which are represented as WORD_C_CUT_MS-DOS, WORD_C_READ_VMS, and WORD_C_ READ ULTRIX, respectively, inherit from method ob~ect 400. For example, in Figure 4, method object 400 may have attributes (not shown) that indicate that the methods, use a certain interaction type, and have a certain server start-up type.
Method object 410 is representative of the CUT
function in EMACS applications. A~ociated with method 410 i~
a set of attributes 430 which includes those inherited from method object 400. Briefly, the PlatformType attribute indicates the platform on which the method ob~ect can be executed. The InteractionType attribute describes the actual type of method which will be executed within a particular method ~erver. Examples of values for this attribute which are explained below, are: BUILT_IN, SCRIPT_ ~i~iKV~;K and DYNAMIC_LOAD. The ServerStartupType attribute indicates an appropriate invocation mechanism to be used for the method server. Example~ of values for this attribute, which are also explained below, are: SHELL, DYNAMIC_LOAD and NAMED_APPLICATION.
The set of attributes 430 specify that the as~ociated method~ operate on platforms which have an 80286 processor with the MS-DOS operating system, and have a BUILT_IN, interaction type, and a NAMED_APPLICATION server start-up type.

Similarly, method object 415 is representative of the READ function in EMACS applications. Associated with method 415 is a set of attributes 435 which include tho8e inherited from method object 400, but which also specify that the associated methods operate on VAX platforms r--nn~ng the VMS operating system, and have an interaction type of l~UILT_IN, and a NAMED_APPLICATION server start-up type.
Method object 420 is a subclass o~ method object 400 representative of the READ function in EMACS applications.
The attributes 440 for method clag~ 420 have a platform type with a MIPS processor running the ULTRIX operating system with a BUILT_IN interaction type, and a NAMED_APPLICATION server etartup type.
Class 450, on the other hand, is a supercla8s of class 460 called FILES, and a class 465 called APPLICATIONS.
Class 460 refers to data objects. As shown in Figure 4, class 460, which would have attributes (not shown), i~ a superclass of class 470. Class 470 is called ASCII_FI~E. For example, class 470 could represent all the files within network 50 (8ee Figure 1) having the common characteristics of ASCII files.
The common characteristics can be described in the attribute8 for class 470, which are not shown in Figure 4.
The class 470 would then be the class for 8everal instances, but the instances are not shown in Figure 4 because they are not managed by the object-oriented architecture.
What is shown in Figure 4 are the messages which the class 470 will support, and the only one shown for purposes of simplicity is the EDIT message 490.

A class supporting a message means that when the message is used as an interface into this object-oriented architecture, it can be used with the cla~s that supports it, and therefore instances within that class. Thus, in the example shown in Figure 4, an EDIT message, can be sent to all instances in the ASCII_FILE class.
APP~ICATIONS class 465 is also a superclass, and one of its subclasses, EDITOR clas8 475, is shown. EDITOR class 475 is a superclass to specific applications classes 480, 483 and 485, corresponding to WORD_ A, WORD_B, or WORD_C. Each of the classes, such as WORD_C 485, repre~ents a specific application, such a~ EMACS or TPU. Thus, each application is defined by one class. An application class may, however, refer to the implementation behavior of more than one application.
The application classes al~o support messages, which is shown by the mes~age CUT 495 being supported by the application class 485. This reflects the fact that at the time of class definition, it was determined that any application represented by the class 485 would have to support a message CUT.
As mentioned briefly above, in the preferred implementation, applications are organized into a hierarchy of classes with a parent class, referred to a~ a superclass, and child classes referred to as subclasses. In Figure 4, class 465 is a superclass called EDITOR. All ~ubclasses of this superclass would have at least the same set of particular unique characteristics or attributes of the superclass. In , . . ... .. . ..

Figure 4, the subclasses of super class 475 EDITOR are WORD_A
480, WORD_B 483, and WORD_C 485. WORD A might represent TPU
applications, WORD_ B 483 might represent all ~SE applications, and WORD_ C 485 might represent all EMACS applications. Each of these subclasses would have, in addition to the characteristics and attributes inherited from superclass 475, their own set of unique characteristics and attributes which differ in such a manner as to enable their separat~on as subclasses within the superclass 475 EDITOR.
In the preferred implementation of this invention, specific rules of inheritance allow for multiple inheritance among classes. This means that any subclass may have more than one superclass. Because this type of inheritance may create ambiguities at definition time, the superclasses are considered to be "ordered" at definition time to resolve potential inheritance conflicts. For instance, at the time of the definition of a subclass described below, if any conflicts arise due to the duplicate definition of a message or attribute in more than one of the listed superclasses, the message or attribute defined in the highest ordered class is considered to be the one inherited by the subclass.
As mentioned above, the relationship between the method ob~ects and the class is by way of method maps. Figure 4 shows two method maps 493 and 498. Each of the classes has messages each of which refers to a specific method map. Thus, method map 493 is associated with EDIT message 490, and method map 498 is associated with the CUT message 495.
Preferably, the method maps include the name of a method object associated with the messages. Method maps could also contain the name of another class and message. Thus, method map 493 includes the name of two method objects.
Method map 493 includes the name of a method ob~ect WORD C_ READ MIPS.ULTRIX 494 which is a name for method object 420, and the name of a method object WORD_C_READ VMS 496, which is a name of method ob;ect 415.
In a similar manner, the method map 498 for the message CUT 495 contains the name WORD_C_CUT 80286.MS-DOS 499, which is the name of the method object 410.
In this way, the method maps 493 and 498 can be used to locate the attribute sets 430, 435, and 440 correspo~;ng to the method objects 410, 415, and 420, respectively. The specific manner in which this type of order is used to locate methods is described in greater detail below.
C. Cla~s Data Base Structure The classes and method objects of the network architecture are stored in a class data base 500 depicted in Figure 5. The class data base 500 represents a nonredundant collection of interrelated data items that can be shared and used by the network 50.
In Figure 4, the class data base 500 consists of two types of objects, similar to what is shown in Figure 4. The objects are either classes 505 or methods 549. Each of the classes 505 corresponds to a generic external representation for the instances of the correspo~ing class. For example, in Figure 5, the class ob~ect ASCII_FILE 506 corresponds to a generic external representation for all members of the set of instances that have the characteristics of the class ASCII
FILE 506. The characteristics are represented by the correspo~; ng set of attributes 510.
In the preferred implementation, the attributes 510 which correspond to the classes 505 may be used in whatever manner the system developer or user wishes. For example, the attributes 511 for the class ASCII FILE 506 may include the name of an icon to represent class 506 on display.
Each of the classes 505 also supports a set of messages 520. A message consists of a "verb" or message name, such as CUT, READ or EDIT, called a selector, and parameters.
Each of the parameters consists of a name and a type and a direction. The name is "typed" which means that the name is of a particular type, e.g., integer, character or string. The possible directions for each parameter may be "in, n nout, ~ and "in/out." When a parameter in a message has an "in"
direction, this means that the parameter is an input to a method to be invoked (discussed below). When a parameter in a message has an "out" direction, this means that the parameter is an output from a method. When a parameter in a message has an "in/out" direction, it means that the parameter is both an input to and output from a method.
The messages 520 are representations for the valid operations that each of the instances represented by the correspo~n~ class 500 can support. For example, in Figure 5, clas~ ob;ect ASCII_FI~E 506 supports the set of messages 520 which includes messages 521 and 525. The specific messages in message set 520 are OPEN (PARA_l, PARA_2...) 521 CA 02049l33 l998-04-09 and EDIT (PARA_l, PARA_2...) 525. For example, in the message EDIT (PARA_1), PARA 1 might repre~ent "FileName: string, in/out," where FileName is the name of the parameter, string is the parameter type, and in/out i8 the direction of the parameter.
Message~ 521 and 525 each refers to respective method map 530 and 540. Each of the method maps 530 and 540 contain~ a set of references to corresponding method objects 549 in the class data base 500 or to the names of other classes and messages. For example, method map 530 contains references 531 and 533 each of which corre~ponds to a different method object (not shown). Method map 540 also contains references 541 and 543, each of which corresponds to a different one of the method objects 549 in the class data base 500. The corresponding method object for the reference 541 is not shown in Figure 5. For purpose~ of this example, Figure 5 does show that the reference 543 on method map 540 refers to the method object 550 which i~ ED 3 READ.
As explained above, the method objects 549 in the class data base 500 are also stored hierarchically. Each o~
the method objects 549 is representative of a reference to executable code capable of performing a method.
In a network data processing system like the preferred implementation, there may be many instances of the executable code associated with each of the method ob~ects 549 and capable of performing the functions identified by each method object. By way of example, in each the memories 150, 250 and 350 (Figure 1) there may be an installation of the .. .... . . . ... . .

.

executable code associated with the method object ED-3_READ
550, with each of the executable codes being capable of performing the functions of the method object ED_3_READ 550 on a respective one of the platforms 100, 200, and 300. The system according to the preferred implementation includes a process which selects between the three executable codes.
Unlike the attrlbutes 510 associated with the classes, the method attributes 560 of the class data base 500 associated with method ob~ects 549 are used to locate and to execute an instance associated with a particular method ob~ect, such as method object 550, in the network. For purposes of simplicity, Figure 5 shows only one set of method attribute~ 561 in the class data base 500. The ~et 561 is associated with the method object 550 of the method objects 549 in the class data base 500. Although some of the method attributes in sets 560, can be arbitrarily specified by the users of the system and used by the system during execution, certain attributes are critical to the operation.
As shown in Figure 5, the method attributes in 8et 561 includes PlatformType = 80286.MS-DOS, InteractionType =
BUILT_IN, and ServerStartupType = SHELL.
In the preferred implementation, two other method attributes are included in the method attribute set 561. One is an InvocationString attribute which defines an invocation string to be used in order to start the ~pecified method server if it needs to be started. The value of this attribute must be a value appropriate for the particular platform 8pecified in the first attribute. For example, if the value :

of the PlatformType attribute is MIPS.U~TRIX and the value of the ServerStartupType attribute is SHELL, then the value of this attribute should be an appropriate ULTRIX shell aommand.
D. Information Flow Before discussing the details of the preferred implementation of this invention, the flow of information throughout the entire system will be explained with reference to Figure 6.
Figure 6 includes a diagram 600 showing different components of the network 50 shown in Figure 1 and the information flowing between those components. Applications 610 and 670 in Figure 6 each correspond to any one of the applications 120, 220, or 320, respectively, and the ACAS
software components 620 and 660 each correspond to anyone of the ACAS software components 130, 230, or 330. The clas~ data bases 640 and the context object data bases 630 are stored in one or more of the memories 150, 250, and 350.
As explained in greater detail below, an application 610, which will be referred to as a "client application, n sends messages. The messages may include instance handles which are the mechanisms used to identify the client (or any other) application' 8 instances. The messages are received by the ACAS software component 620 in the client platform.
ACAS software component 620 then uses the names of the messages and the classes of the instances referred to by the instance handles to find the method maps in class data bases 640. ACAS software component 620 may also use context information from context ob;ect data bases 630 to select a method identifier from the method map which identifier represents the method to be executed. The context information is also used to select a platform, called the "server platform," on which to execute the selected method. The context information will be described in detail below.
ACAS software component 620 sends the method identifier retrieved from the class data base 640 and the instance handles to an ACAS software component 660 in the server platform. Thereafter, the ACAS software component 660 takes the appropriate steps to execute the identified method using a "server application" 670 or informs the ACAS software component 620 that the server platform containing ACAS
software component 660 cannot respond to the request. In this latter case, the ACAS software component 620 then reviews the context information to select another platform in the network as a server platform or else informs the client that the request has failed.
If the execution of the method identified in Figure 6 by the server application 670 generates a message to be returned to the client application 610, then that message along with additional information i8 passed from server application 670 to ACAS software component 660 in the server platform. ACAS software component 660 in the server platform then sends responses to ACAS software component 620 in the client platform, which relays those responses to the client application 610 in the client platform.
All these transactions will be described in greater detail below.

E. MemorY SYstems (1) Global Class Data ~ase A diagram of the entire memory system 700 is shown in Figure 7. Memory ~y~tem 700 includes a global class data base 705 and local class data bases 710, 730 and 750. A
network-wide memory 705 is also provided to make certain other information, described below, available to u~ers of the network.
Global class data base 705 contains information accessible by all of the platforms. Preferably, global class data base 705 is distributed throughout the memories of the platforms. For example, in Figure 7, global class data base 705 is shown as being partially resident in each of memories 150, 250, and 350. The remainder of the global class data base 705 would be resident in other memories which are not shown in Figure 7. The contents of the global class data base 705 have already been described with regard to Figures 4 and 5.
Persons of ordinary skill in the art will recognize that the diQtributed memory arrangement shown in Figure 7 is not required to practice the present invention. For example, the entire global cla~s data base 705 could be stored in the memory of a single node or in a dedicated memory, without affecting the principle~ of this invention.
In addition, each of the memories 150, 250, and 350, i~ shown a~ having a local cla~s data base 710, 730, and 750 as well as a node cache 720, 740, and 760, respectively. The information in the local class data bases is accessible only by users on the corresponding platform. Node caches 720, 740, and 760 are used to hold a copy of portions of global class data base 705 which are accessed frequently by the corre8pon~ ng platform.
The data base system used to implement the global class data base structure should support global uniqueness of names within a single data base, uniqueness of identifiers across data bases, access control mechanisms, and proper storage and retrie~al mechanisms. Global name uniquene~s is important for objects because they are generic. Identifier uniqueness allows data bases to be combined, as explained below.
Access control mechanisms of the data base system must allow an authorized user on any platform in the network to store and retrieve objects and attributes, and must provide security control and syntax checking to avoid compromising the integrity of global class data base 705. Some of the details of this control are discussed below. The remainder involve well-known data base management techniques.
The preferred implementation requires that each object in global class data base 705 can be assigned an object identifier which, like an object name, can be used to refer to an object. Object identifiers are also preferably language neutral becau~e they are binary codes.
Object identifiers are assigned based upon a "globally" agreed-upon scheme, and are unique throughout any number of class data bases. Object names, on the other hand, need be unique only within a single class data base. The differences between the class names and identifiers can be better appreciated by an example. Assuming two companies each have their own cla~ data base and wish to merge those data bases, those data bases may have classes with the same names which should be different in the merged data base, and that difference can be maintained through the globally-unique identifiers. The data bases may also have two classes with different names which should be the same in the merged data base. Those classes can be set to have the same clas8 identifier. Thus, the object identifiers also permlt the same cla8s in the global class data base to be identified by more than one class name. For example, the class name EDITORS in the global class data base in the network may also be identified by the class name WPROCESSORS.
Another software component which is also included in each of the ACAS software components 130, 230, and 330, provides the mechanism to create a unique object identifier for use and storage in the class data bases. Preferably, any storage scheme employed by an application which requires the persistent storage of object names should store the object identifiers rather than the object names to avoid naming conflict~ between multiple global class data bases.
The global class data base 705 is not meant to 8tore application instance data because preferably applications completely manage their own sets of application instance data.
This allows existing applications to continue their current storage strategies, and does not restrict the 8torage optlons available for new applications.

The preferred implementation provides two mechanisms, however, storage classes and instance naming, which enable applications to link their privately managed instances with the global clas~ data base 705 maintained by the preferred implementation.
Storage classes are an abstraction that allow an application to specify how privately managed instances are to be interpreted. The storage classes give an alternative to identifying the class of each instance when the instance is used in a message. In the preferred implementation, storage classes identify storage systems, such as repositories or files, which contain names of instances. For example, a storage class can describe a known storage mechanism such a~
"RMS_FILE" or "UNIX_FILE."
In the object-oriented architecture of this invention, storage classes are also con8idered to be cla8se~.
Similar to other classes stored in the class data base, the storage class can be viewed as an actual object-oriented class definition that consists of attributes, messages, and methods.
The methods as~ociated with each storage class are u~ed to retrieve the class name for an instance associated with the particular storage system identified by the instance'c storage class.
The other mechanism, instance naming, employ~ a st~n~Ard for the naming of instances in the preferred implementation. The standard instance handle is a ~tring ropre~ented by the following logical structure~
cclass~storage class~clocation~cin~tance reference_data~

,. . - .,: ;

. .

The term "class" is the name of the associated ACAS class.
The term "storage class" is an alternative to the class name and is the name of the storage class. The term "location" is the logical location, such as the node, of the instance. The "location" is optional and will be used if a client desires a method to run at the same location as the instance i8 located.
The term "instance_reference_data" is the application private portion of the instance handle.
Instance handles allow implementations to refer to instances abstractly, thereby avoiding the need to manage the instances themselves.
The instance handle preferably includes the class or ~torage cla88 (if necessary), location of the instance, and the identifier for the instance. For example, in the message:
EDIT (INSTANCE_HANDLE) EDIT repre~ents the desired operation. The INSTANCE HANDLE
string could be ASCII_ FILE/NODE 1/MYFILE.TXT. In this instance handle, ASCII FILE represents the class, NODE 1 is the location of the instance, and MYFILE.TXT is the identifier of the instance. This message provides sufficient class and message information to find the proper method map. It will be apparent to those of ordinary skill in the art that other formats may be employed for the INSTANCE HAND~E string to accomplish the same objectives as the preferred implementation does.
As explained above, all classes in a global clas~
data base of the preferred implementation have unique names with the particular global class data base. The class name i8 generally assigned by the user who first defines the class.
(2) Local Class Data Bases In addition to a global class data base, the preferred implementation also supports local class data bases for class and method definitions. The local class data bases function similar to the global class data base, except the contents of the local class data bases are not globally available. They need only be available for their local node.
Thus, the local class data bases need not be distributed or replicated in other nodes.
Figure 7 shows a preferred implementation of the local class data bases 710, 730, and 750 in memories 150, 250 and 350, respectively. The local class data bases 710, 730 and 750 hold the class and method information created by the corresponding nodes which has not yet been added to the global class data base.
In the preferred embodiment, memories 150, 250 and 350 also contain node caches 720, 740 and 760, respectively, which hold method and class information loaded from global class data base 705. Caches are an optimization and are not strictly required.
The data base system ~sed to implement the local class data base must provide name uniqueness within a single data base. Access control for the local class data base is only required at the data base level. The preferred implementation of a locàl class data base relies upon the underlying security mechanisms within the data base system to control access to the contents of the local class data base.

Use of the local class data base provides several advantages over use of the global class data base. For example, the local class data base provides the ability for applications on each node to continue to communicate with each other in an ob~ect oriented manner even when the network is unavailable. In such a situation, applications on the node can continue to invoke other applications that are local to that node.
In addition, using a local class data base provides better performance for applications that reside in the same node as the local class data base because many invocations can be handled completely within the confines of a single platform. On platforms in which moat applications will most likely use invocations that can be handled locally, use of the local class data base may eliminate or greatly reduce the need for network activity, such as accessing the global class data base, to accomplish an invocation.
The class data bases are preferably searched for clas~ and method information by searching the local data bases before searching the global data base. The local data bases of each node are preferably searched in a predetermined order as explained below. AB soon as the desired information is located, the search stops. Only if the desired information cannot be located in local data base is the global data base searched. Thus the search order defines the "priority" of the class data bases.
Figure 8 shows one design of a portion of a local cla8s data base 800. This design, however, is not cr~t~cal to the invention. Preferably local class data base 800 contains a data base header 810 which is used to locate other organizational information in the local class data base 800 such as indices and allocation maps. Local class data base 800 also includes a block storage space 815 contA;n;n~ a number of blocks 820, 822, and 824 which hold the information about the classes and methods.
Figure 9 shows a preferred arrangement of block 900 which could be block 820, 822, or 824. Block 900 includes a directory 910, located at the beginning of block 900, to ident~fy the location of the objects within the blocks, and an ob~ect storage portion 920.
Entries 955 and 965 in directory 910 each correspond to a different object 950 and 960 located in object storage portion 920 of block 900. Each directory entry includes a value for an ID field 912, which identifies the correspo~;ng ob~ect, a value for an OFFSET field 915, which represents the relative location of the corresponding object in the block 900, and a value for a SIZE field 917 which indicates the amount of block 900 allocated to the correQpo~n~ object.
Ob~ects 950 and 960 are preferably formatted as character string, although other techniques can be used.
Referring again to Figure 8, local class data base 800 preferably contains a NAME-TO-ID-INDEX 830 which allows ob~ects to be retrieved by correlating their name to object identifiers.
The object identifiers are included in the ID-TO-BLOCR NO. MAP 840. The map 840 provides block numbers for each unique object identified in the local class data base 800.
The remaining field in the local class data ba~e 800 is BLOCg TABLE 850. BLOCK TABLE 850 preferably includes the locations of the blocks 820, 822, and 824 and the locations of the available space 829 within the local class data base 800.
A~railable space 829 i8 the unused space of the block storage space 815 allocated by the local class data base 800.
To retrieve an object from local class data base 800, the name for that object i8 mapped to the NAME-TO-ID-INDEX 830. The identifier information from the NAME-TO-INDEX 830 is then mapped to the appropriate block number using the ID-TO-BLOCK NO. MAP 840. The mapping yields the block number where the desired object currently resides.
Once the block with the desired object i~ located, the ob~ect is found using the object directory 910 (Figure 9).
(3) The Loader/Unloader As shown in Figure 10, preferably a LOADER/UNLOADER
software component 1010 i9 coupled between a local class data ba~e 1000, a global class data base 1020, and a node cache 1030. The LOADER/UNLOADER software component 1010, which is part of the ACAS ~oftware components 130, 230, and 330 ~Figure ), i8 used to control the transfer of ACAS information to and from the local data base 1000, the node cache 1030, and the global class data ba~e 1020. In the preferred implementation, the LOADER/UNLOADER software component 1010 permits the local class data base 1000 to load information into the global class data base 1020, and permits the node cache 1030 to retrieve class data base information from the global class data base 1020. During loading and unloading the LOADER/UNLOADER
component 1010 preferably uses memory 150 for storage.
The LOADER/UNLOADER software component 1010 is activated by a user wishing to transfer class information in local class data base 1000 to the global class data base 1020.
The transfer makes information previously accessible only to the platform accessible to all network users through global class data base 1020. Transfer of class information from the local class data base 1000 to the global cla~s data ba~e 1020 i8 preferably achieved by sending class and method ob~ect definitions in an ASCII format to the LOADER/UNLOADER software component 1010 for loading into the global class data base.
The LOADER/UNLOADER software component 1010 preferably execute~ a process to parse language definitions stored by the local class data base, and translates those definitions into an appropriate ASCII representation. The LOADER/VNLOADER 1010 then formats this ASCII representation to be stored in an appropriate format by the global class data ba~e.
LOADER/UN~OADER software component 1010 mu8t also respond to re~uests from the user to unload or to retrieve information from the global class data base 1020 for loading into node cache 1030. The retrieved information is preferably translated by the LOADER/UNLOADER ~oftware component 1010 ~nto language definitions which are 8tored into the node cache 1030.

. , F. Creatinq Defininq/Reqisterinq Cla~se~ and Methods (1) Creation Preferably classes are defined using non-procedural language, such as that used in the LOADER/UNLOADER, and are then compiled and loaded into a class data base. The language, compiler and loader software are preferably components of an object definition facility. Other well-known techniques would also be apparent to those of ordinary skill in the art.
The ob~ect definition facility i8 part of the ACAS
software components 130, 230, and 330 (Figure 1) and provides a means to define classes, messages, class attributes, methods and method attribute~. This facility also provides for the specification of inheritance among clas~es and, along with the LOADER/UNLOADER software component 1010 described above, can be used to modify existing definitions within the global class data base and the local class data base. In addition, the object definition facility preferably performs the necessary syntax checks of class definition input and method definition input used to create new class and method definitions within the global class data base.
A user of the object definition facility must specify certain information to create a class. This information preferably includes: a global class name and identifier; global names and identifiers (if any) of the superclasses of this class, messages supported by this class, along with their associated types of arguments (if any) method maps defined and the messages to which each map relates; and attributes defined for this class.
Each message is preferably specified by generating a 8tructure including the name of the message, parameter8 supported by the message, and a corresponding method map.
Each message structure is converted into two sets of values in the preferred implementation. One set of values includes the message name and the list of parameters supported by the message. The other set of values identifies a 8et of method ob~ects that represent implementation~ of the message.
Method objects are defined within the network environment in the same manner as classes. The ob~ect definition facility of the preferred implementation, however, has special provisions for defining of method ob~ects. The following information is specified when defining a method ob~ect, the global name and identifier of the method ob~ect;
global names and identifiers of the superclasse8 of the method ob~ect; and metadata (i.e., descriptions of data) stored a8 the method attributes. The method definition also specifies the arguments and their types corresponding to the parameters in the message, and whether the method involves a parameter list. This parameter list represents the input required by the executable code (discussed below) capable of being invoked by the method.
(2) Method/Class Definition In the preferred implementation, the loading of class and method definitions may either be done prior to run-time or dynamically during run-time. Classes and method ob~ects may be accessible either locally on a node within the network (called "local definition") or globally from all platforms in the network (called "global definition"). Both local and global definition can be accomplished using the LOADER/UNLOADER software component 1010 or any other acceptable mechanism.
(3) Server Reqistration The purpose of server registration i8 to find method servers which are available to service requests from messages.
Method servers are the active (i.e., currently rnnn~ng) processes implementing the methods. A method server may involve execution of the code of a single application or of many portions of the code of one or more applications.
The registration of method servers is distinct from the definition of classes and method ob~ects. Whereas the definition of classes and method objects is used to identify their presence in the system, the registration of method servers is used to track their status (i.e., availability).
If a method server is not registered, it is not known to the system.
(4) A~plication Installation & Definition Preferably, support mechanisms are provided for registering and installing applications in the network. The preferred implementation provides the ability to define applications and application fragments in the ob~ect-oriented model of classes, subclasses, messages and methods stored in a class data base. The definition of applications in this manner is critical to the operation of the interapplication communication performed by the preferred implementation of ; .

this invention. Specifically, the storage of classes, subclasses, messages and method~ in a claQs data base permits an application, during run-time, to update the claQ~ data base and continue processing using the updated class data base without having to recompile and relink.
Applications are defined in the same manner as other classes. In fact, as explained above, an application is itself defined to be a particular kind of class.
Applications are installed on specific platforms in the manner required for the particular operating system on that platform. In the preferred implementation of this invention, application installation also requires some additional functions. For example, unless it has already been defined, an application must provide its own class definition which is defined as a subclass of the existing ACAS_APPLICATION.
Application installation may use class definitions already installed or may add new definitions. At application installation time, an installation procedure may compile and register the class definitions supported by the application into either a local class data base or the global class data base using the LOADER/UNLOADER software component 1010 described above, and must update the method maps of the data ob~ect classes affected by the new applications. Application installation also involves the method object definition procedures discussed above.
G. Context Ob~ect Data Bases In the preferred implementation of this invention, context ob~ect data base 630 (see Figure 6) provides a mechanism to define preferences to be used for resolving methods, for selecting platforms to execute a method, and for locating class data bases in the network. Several levels of context object data basee can exist in the network 50 of Figure 1. For example, one le~el may consist of a user context object data base and another level may consist of a group context object data base. System (or platform) context ob~ect data bases may also be used to identify preferences for users of the entire platform. All context object data bases supply preferences during method resolution, but, the group context object data base may be used by the ACAS software components 130i 230, and 330 to recognize the preferences of more than one user, and the system context object data base may be used to recognize the preferences of more than one group. Preferably, the data bases in context ob~ect data base 630 are used such that in method resolution, preferences in the user context object data bases override those in the group context object data baseR, which in turn overrides the system context object data bases.
Context object data base 630 preferably resides on the platform associated with a user during a particular network session. In the initial log-on procedure executed when a user enters the network, the informatlon stored in the context ob~ect data base associated with the u8er is called up for later use during the operation of the ACAS software.
Figure llA shows a preferred memory system for a context object data base 1100. The context object data base 1100 includes a method override table 1110, a server node table 1150, and a class data base override table 1170, and other user defined tables 1180. The method override table is used dur~ng method resolution, described in detail below, to select a preferred method in response to a message name and a class identified in an instance handle. The server node table 1150 is used during the invoker operations, also described in detail below, to select and locate platforms in the network capable of being a server platform. Class data base override table 1170 defines an order for searching the local class data bases for method and class information.
Tables 1110, 1150, and 1170 are system-supplied tables. Users may also supply their own tables 1180 to effect their specific preferences.
A preferred implementation of a method override table 1110 is shown in Figure llB. Method override-table 1110 includes a list of method selector attribute names 1115 and associated values 1120. Each entry specifies for an attribute name 1115, a preferred value 1120. For example, in Figure llB, the preferred platform is specified as a VAX.VMS, and the preferred interaction type is BUI~T_IN. If more than one method is identified in response to a message, the preferences in table 1110 will be used to choose one of those methods. If no value is specified for an attr~bute, the system assumes there is no preference.
A preferred implementation of a server node table 1150 of the context object data base 1100 is shown in Figure llC. Server node table 1150 is an ordered list of nodes in the network 50 of Figure 1. Each of the entries in table 1150 corresponds to a platform type 1152 and the location of nodes 1154 in the network 50 with the corresponding platform type which can be used to implement the selected method. For example, table 1150 identifies two nodes for a platform type of TYPE A, node a and node b.
Figure llD contains a preferred implementation of class data base override table 1170. Table 1170 includes several entries which include a name of a local class data base 1172 and its location 1174. Thus, for entry 1175, the data base DB_SCH_LST i8 at locations dbl and db2, and is searched before other local class object data bases listed further down table 1170.
The preferred implementation of the pre~ent invention includes an interface available to all users of the network which provides the capability to create context ob~ect data bases and to add, modify and delete entries within each of the system context object data bases. This interface preferably executes a standard compiler to perform these functions. For example, to add an entry to a context ob~ect data base, a user would enter a com~-n~ using the provided interface. The command would then be interpreted by the ACAS
software components 130, 230, and 330 (Figure 1) to cause the stAn~rd compiler to translate the data received by the interface into the proper formats.
H. ACAS Service (1) General OPerations With the preceding description of certain components CA 02049l33 l998-04-09 .

of the preferred implementation of thi~ invention, a fuller underst~ntl~n!J of the ACAS components may be gained.
Preferably, the present invention is implemented using a client/server model in which a client generates requests and a server responds to resluests. In the following discussion, the service or operation associated with a client application on a client platform is called the "client service," and the service or operation associated with a server application executing on a server platform is called a "server service."
The client service and the server service of the preferred implementation rely upon a tran8port system which is capable of transmitting mes~ages from the client platform to and from the server platform. In the preferred implementation, an RPC-like communications system is used as the transport system.
Each of the ACAS software components 130, 230, and 330 shown in Figure 1 preferably includes client service components and the server service components which represent the client and server services, respectively. This is shown, for example, in Figure 12 which is a diagram of two platforms 1200 and 1300 and a network bus 55. Platforms 1200 and 1300 can correspond to any of platforms 100, 200, or 300 in Figure 1.
Located in platforms 1200 and 1300 are memories 1250 and 1350, respectively, and CPtJs 1210 and 1310, respectively.
The elements in the platforms 1200 and 1300 function in the same manner a~ similar elements de8cribed above with reference to Figure 1. CPU 1210 executes a client application 1220 and CPU 1310 executes a server application 1320. CPUs 1210 and 1310 also execute OP SYS 1 1240 and OP SYS 2 1340, respectively, and ACAS software components 1230 and 1330, respectively.
ACAS software components 1230 and 1330 preferably include dispatcher software components 1232 and 1332, respectively, control server software components 1234 and 1334, respectively, invoker software components 1236 and 1336, respectively, and the auxiliary software components 1237 and 1337, respectively.
For the most part, invoker software components 1236 and 1336 represent the client service and dispatcher software components 1232 and 1332 represent the server service. The auxiliary software components 1237 and 1337 represent some other operations of the preferred implementation. Since platforms 1200 and 1300 in the network contain an invoker software component 1236 and 1336, respectively, a control server software component 1234 and 1334, respectively, and a dispatcher software component 1232 and 1332, respectively, either platform can act as a client or a server.
In the preferred implementation, the invoker software components 1236 and 1336 and the dispatcher #oftware components 1232 and 1332 have the responsibility for ~ nterpret~ ng cla~ and method lnformat~ on ln th~ clans~ data bases, as well as context data in the context ob~ect data base, to determine the appropriate method to invoke, to determine how to invoke that method, and to dispatch the necessary commands to execute the code to implement the method. The invoker software components 1236 and 1336 and the di~patcher software components 1232 and 1332 also insulate client applicationQ- from the detail~ of the method invocation and the transport level mechanisms.
The control server software components 1234 and 1334 have several functionQ. One function i~ to store information on currently running server applications on the platform8 1200 and 1300 in the network 50. The control server software components 1234 and 1334 al~o execute processes to start new applications that become method servers. Another function performed by control server software components 1234 and 1334 is method server registration. For example, the control server software component 1334 stores information regarding the method server, identified by the server application 1320, currently running on the server platform 1300. The control server software component 1334 also communicates with the server regi6tration facility in network-wide memory 704 (Figure 7) to store status information regarding the server application 1320.
The auxiliary software components 1237 and 1337 represent operations of the ACAS software components 1230 and 1330 such a~ class and method object definition and registration, method executable registration (de8cribed below) in a method executable catalog of each platform, and funct~ons of the LOADER/UNLOADER software component 1010 (Figure 10).
For purpose of the following discu8sion, the platform 1200 is referred to as the client platform and the platform 1300 is referred to as the server platform. In this example, the client application 1220 communicates with the server application 1320 in the server platform 1300 in an ob;ected-oriented fashion. It is also possible in accordance with the present invention and in the preferred implementation for a client application on one platform to communicate with a server application on the same platform.
When the client application 1220 communicates with the server application 1320, the dispatcher software component 1232 and control server software component 1234 of the client platform 1200 is not involved, and are therefore shaded in Figure 12. Likewise, invoker software component 1336 of the server platform 1300 is shaded because it is not active.
Figure 13 is a flow diagram 1360 outlining the major functions performed in an invocation of a method according to the preferred implementation. Prior to beg~ nn~ ng the steps in flow diagram 1360 the ACAS software components 1230 and 1330 are initially in a "wait" state.
When the client application 1220 transmits a method invocation request, the processes of the ACAS software components 1230 and 1330 shown in Figure 13 begin. This method invocation request includes an input message which identifies the desired operation of the client application 1220.
First, the method in~ocatlon ~équest is received by the invoker software component 1236 (step 1370) which processes the method invocation request (step 1375). The invoker process is described in greater detail below. The usual result of the invoker process is a processed method invocation request.
The invoker eoftware component 1236 then transmits the processed method invocation request, via network bus 55 to the dispatcher software component 1332 (step 1380). The dispatcher software component 1332 and control server 1334 then begin their operations.
After receiving the processed method invocation request, the dispatcher software component 1332 and control server software component 1334 cause the method identified by the invocation request to be executed by the server application 1320 (step 1390). Once the server application 1320 completes execution of the method, it outputs any arguments resulting from the execution and the dispatcher software component 1332 generates a status message (e.g., "successful"). The output arguments and status message are mapped into the processed method invocation request, now called a "response." This response is then transmitted by the dispatcher software component 1332 to the invoker software component 1236. The invoker software component 1236 completes its processing by returning the responsé received from the dispatcher software component 1332 mapped into the original method invocation request, to the client application 1220 (step 1395).
The preceding explanatlon of the ACAS software components 1230 and 1330 permits a greater appreciation of the flow of information in the preferred implementation of this invention. Figure 14 shows additional elements of the network 50 affected by a flow of information from the invoker software .

component 1236 to the dispatcher software component 1332. In addition to the client application 1220, the server application 1320, the invoker software component 1236, the dispatcher software component 1332, and the control server software component 1334, Figure 14 includes context object data bases 630 (Figure 6), class data bases 640 (Figure 6), a server registration facility 1420, and a control server registry 1425, which is maintained by the control server software component 1334 and keeps track of the executable code in the server platform.
As shown in Figure 14, the context object data bases 630 includes a user context object data base 1402, a group context object data base 1404, and a system context ob;ect data base 1406, each of which has been described above in the discussion of context object data bases. The class data bases 640 include a local data base 1000 (Figure 10), a node cache 1030, and a global class data base 1020. Each of these elements of class data bases 640 has been described above in the discussion of class data bases.
As explained above, the flow of information begins when client application 1220 generates a method invocation request which is passed to invoker software component 1236. This interface is preferably provided by an InvokeMethod procedure call of the preferred implementation.
In the InvokeMethod proced~re call, the client application 1220 passes to invoker software component 1236 an instance handle, a message (including a message name, and parameter list), a context object handle, and, optionally, an output instance handle.
As discussed in detail above, the instance handle is a structure that identifies the current instance the client application 1220 has selected to be involved in the method invocation. The message name represent# the desired operation on the instance. The message parameter list consists of the parameters required by the message. The context object handle is a reference identifying the context object data base to be used in the invocation process described in detail below. The output instance handle represents an instance of the rl~nn; n~
method server associated with the invoked method. This allows the client application to continue to have a dialogue with the same method server. The semantics of the output instance handle is the same as that for the instance handle.
When the invoker software component receives the method invocation request, the invoker software component 1236 gueries the context object data bases 630 and the class data bases 640 to find a method identifier. This procedure has been discussed above.
Having determlned the appropriate method identifier for the message name, the invoker software component 1236 next gueries the server registration facility 1420 and the context object data base 630 to find the server platform on which to execute the method associated with the method identifier. The server registration facility 1420 is used to locate a rl~nn;ng method server (if any) capable of performing the method associated with the method identifier. A rllnn; ng method server is a method server, such as the server application 1320, that has made itself known to the network 50 as being already started.
If there is a running method server, the invoker software component also queries server platform tables of the context object data base 630, to determine the location of a remote platform in the network 50 (Figure 1) which the user of the client application 1220 would prefer to execute the method of invocation request processed by the invoker software component 1236. If however, the server application 1320 is not available, the control server software component 1334 notifies the invoker software component 1236 that the server application is not available on the selected remote platform.
The invoker software component 1236 processing outlined above begins again with querying the server platform table of the context object data bases 630 and server registration facility 1420 to select another platform in the network 50 upon which to execute the identified method.
Next, the invoker software component 1236 transmits a query to the control server software component 1334 of the preferred server platform which causes control server software component 1334 to query a control server reglstry 1425 to determine whether the desired method server on the preferred server platform is available to process the method identified in the processed method invocat~on request. Availability of a method server is determined in the preferred implementation by examining in the control server registry 1425 to find out whether the method server is currently able to process methods invoked by client applications.

If the control server ~oftware component 1334 indicates to the invoker software component 1236 that the method server, in the form of server appl$cation 1320, is available, the invoker software component 1236 transmits the proces~ed method invocation request to the dispatcher software component 1332 of the server platform. The invoker software component 1236 can also transmit information from the context ob~ect data base 630, which can then be used by the desired method server.
The dl~patcher ~oftware component 1332 then begins to process the desired method. This process, referred to as the "dispatching process,~ generally involves dispatching the method identifier to begin the execution of the method by the server application 1320.
If, however, the server registration facility 1420 does not indicate that any copies of server application 1320 and currently rllnn; ng on a platform in the network, then the invoker software component 1236 may transmit a request to the control server software component 1334, using the information retrieved from the context object data bases 630 and the class data bases 640, to start the server application 1340. After the server application 1320 is started, the control server software component 1334 notifies the server registration fac~l~ty 1420 to update the network-wide memory 704 (Figure 7) to indicate that the server application 1320 ig rl-nn;ng.
Control server software component also updates the control server registry 1405 to indicate that the server application 1320 is available. The invoker software component 1236 then transmits the processed method invocation request to the dispatcher software component 1332 to execute the method corresponding to the method identifier of the processed method invocation request.
After the server application 1320 has completed it~
processing, it returns any output information requested by the processed method invocation request to the dispatcher software component 1332. The dispatcher software component 1332 then returns a response, as described above, to the invoker software component 1236 along with any output information mapped into the output arguments of the processed method invocation request received by the dispatcher software component 1332.
(2) Invoker Operation The portion of the process of method invocation performed by the invoker software component 1236 can now be described in greater detail. Preferably, that portion consists of several distinct phases including determin~ng the proper method to be invoked (method resolution), server connection or start-up, and transport level commun~cations to enable the dispatching of an identifier to the proper method to be executed by the method server or other executable code.
Figures 15A - 15D and 16 contain flow diagram~ of procedures performed or called by the invoker 80ftware component 1236 of Figures 12 and 14. The main control procedure 1550 in Figures 15A - 15D represents the 8teps 1370, 1375, and 1380 (Figure 13) performed by invoker software component 1236.
As with procedure 1360, prior to entering the main control procedure 1550, the client application 1220 (Figures 12 and 14) i8 rllnn~n~ normally without a method invocation request, and the ACAS software component 1230 is in a "wait"
state. When the client application 1220 generates a method invocation request using the InvokeMethod procedure call, the main control procedure 1550 begins (step 1552 in Figure 15A) with the invoker software component 1236 receiving the method invocation request (step 1555).
The invoker software component 1236 first validates the method invocatio~ reguest (step 1557). If there was an error, the invoker software component 1236 generates an error message (step 1558) which the invoker software component 1236 returns to the client application 1220 (step 1599 in Figure 15D).
If the method invocation request is valid (step 1557 in Figure 15A), the invoker software component 1236 next resolves the method to be invoked from the message in the InvokeMethod call, the class data bases, and context ob;ect data bases (step 1560). Method resolution is the process of determining or identifying the appropriate method.
Figure 16 shows a preferred procedure 1600 to resolve methods. Although method resolution has been referred to above, procedure 1600 shows such resolution in much more detail than has been provided.
In the preferred implementation, the determination of the proper method to be invoked is indirectly handled by the invoker software component 1236. Most of the work for method resolution is then handled by the auxiliary software components 1237 and 1337 of the ACAS software components 1230 and 1330. In the preferred implementation, auxiliary software component 1237 retrieves information from the context ob~ect data bases and the class data base~. Of course, invoker software component 1236 could also retrieve such information.
After beginning the method resolution procedure 1600 (8tep 1605), the invoker software component 1236 determines whether the instance handle includes the storage class name portion (step 1610). If a storage class exists, it i8 located (step 1620) and a special method is invoked to retrieve the name of the class associated with the instance handle (step 1630).
After invoking the method identified by the storage class to retrieve the class name, or after determining that the instance handle did not include the storage class name, a proce8s is executed by the invoker software component 1236 to locate class information for the class data bases 640 (Figures 6 and 14) using the searching order described above (step 1640). For example, if the message was EDIT
(INSTANCE_HANDLE), where the instance handle was ASCII_ FILE/NODE_l/MYFILE.TXT, the class name ASCII_FILE can be u8ed to find class ASCII_FILE 1645 in cla~s data base8 640.
With the name of the message, EDIT, the appropriate method map 1655 i~ then retrieved from the class data bases 640 (step 1650). In the specific example under discussion, the auxiliary software component 1237 of the preferred implementation would then retrieve method map 1655 and check to ensure that the class information located in step 1640 lncludes with the mes~age name EDIT. Thi~ ensures that the cOrre8pO~; ng message is supported by the class.
As Figure 16 shows, the method map 1655 includes method objects METHOD 1 and METHOD 2 for the message name EDIT
and the class ASCII_FILE 1645. Associated with the method ob~ect METHOD 1 is a set of attributes 1657 and associated with method object METHOD 2 is a set of attributes 1659. The set of attributes 1657 indicates that METHOD 1 is capable of being executed on PLATFORM_ TYPE A, and the set of attributes 1659 indicates that METHOD 2 is capable of being executed on PLATFORM TYPE B.
Because there might be several method objects in the method map, the context object data bases 630 are referenced to resolve any ambiguities (step 1660). In referencing the context object data bases 630, the appropriate server node table maintained is also retrieved to be used later.
The entries (if any) in the context object data bases 630 are then compared with the attributes in set of method objects on the method map (step 1670) to select the method ob~ect and thus the appropriate method to execute the desired operation represented by the message (step 1680). In Figure 16, a method override table 1665 includes an entry 1668 indicating the user preference is for PLATFORMTYPB A. Using this entry 1668 the invoker software component 1236 8elects from the class data bases 640 the appropriate method 1686 to execute the desired operation EDIT. In the example shown in Figure 16 the appropriate method is Method 1 to be executed on PLATFORM_TYPE A. The procedure 1600 now returns to the main control procedure of 1550 of Figure 15 (step 1685).

If at any point during the operation of method resolution procedure 1600, there is an error (such as during-step 1640, the class identified in the instance handle was not a class locatable in the class data bases), the method resolution procedure 1600 returns with a message indicating this error.
After returning from the method resolution procedure 1600, a determination iB made whether an error occurred during the method resolution process (step 1562 in Figure 15A). If the answer is "yes", then the invoker software component 1236 ge~erates the appropriate error message (step 1563), and returns the error message to the client application 1220 (step 1599 in Figure 15D).
Otherwise, having resolved the method without error (8tep 1562 in Figure 15A), the invoker software component 1236 then reviews the method attributes corresponding to the identifier of the resolved method to execute the appropr~ate method on an appropriate platform in the network. If these method attributes indicate that the method is already linked into the client application 1220 (step 1565 in Figure 15B), for example, the value of the InteractionType method attribute i~ "BUILT_IN," then a check is made for an activation error (step 1566). If there was one, an error mes~age is generated (step 1576) and control iB returned to client application 1220 (step 1599 in Figure 15D).
If there was no error, a succes~ flag i8 generated (step 1567), and the resolved method is executed by code already resident in the client application 1220 (step 1569).
If the method attributes do not indicate that the .... . . ..

method i~ already linked to the client application 1220 (8tep 1565 in Figure 15B), invoker software component 1236 asks whether the method attributes indicate that the method is dynamically loadable (step 1570). Dynamically-loadable methods repreRent method executables which may be merged with executable code of client applications at run-time. Those skilled in the art will recognize that a dynamically-loadable method might be a method executable identified by a subprocedure or function of a client application. Preferably the test for a dynamically-loadable method server is accomplished by determ; n; ng whether the value of the InteractionType method attribute is "DYNAMIC_LOAD." If 80, then the invoker software component 1236 attempts to load the executable code identified by the resolved method into the client application 1220 (step 1572).
If an error occurred during the loading of the executable code (step 1574), then the invoker software component 1236 generates a message indicating that a load error occurred (step 1576) and returns the load error me~sage to the client application 1220 (step 1599 in F~gure 15D).
Otherwise, if there was no load error (step 1574), then the invoker software component 1236 then generates a flag indicating the successful completion of the method invocation (~tep 1567). Next, the dynamically loaded executable code corresponding to the resolved method is executed (step 1569), and control returns to the client application 1220 along with any output arguments (step 1599 in Figure 15D). Any errors in executing linked or dynamically-loadable method servers are preferably returned as parameter values.
If the method attributes do not indicate a previously-linked or dynamically-loadable method (steps 1565 and 1570 in Figure 15B), then the invoker software component 1236 mu~t locate a running method server on a platform in the network that can handle the resolved method as described above with regard to Figure 14.
If the information retrieved from the server registration facility 1420 (step 1578) indicates that there is at least one running method server capable of performing the method identified by the resolved method (step 1579 in Figure 15C), then the invoker software component 1236 compares the information retrieved from the server registration facility 1420 with the entries on the server node table retrieved from the context object data bases 630 during the method resolution procedure 1600 to select a server platform in the network (~tep 1580).
Having selected a server platform, the invoker software component 1236 then transmits a QueryServer call to the control server software component 1334 of the selected server platform (~tep 1581). The functioning of the control server software component 1334 is described in detail below in connection with Figure~ 17A and 17B. Briefly, control server software component 1334 determines whether the desired method ~erver is available or not.
The main control procedure 1550 of the invoker software component 1236 then continues in step 1582 (Figure 15C) by receiving a mes~age generated by the control server software component 1334 about the desired method server's availability and translating the mes~age into a format recognizable by the client platform. The invoker software component 1236 determines from the control server software component 1334 whether the method server corresponding to the resolved method is available to process the method identified by the resolved method (step lS83). If the corresponding method server is available, then processing of the invoker software component continues on Figure 15D by asking whether the method server is an asynchronous method server (step 1593) in Figure 15D. Asynchronous method servers are known in the art.
If the method server is asynchronous (step 1593), then the control server software component 1334 is called using the SignalServer call to signal the method server (step 1594). If the method server is not asynchronous (step 1593), or after an asynchronous method server is signaled (step 1594), the processed method invocation request, including the identifier for the method and information retrieved from the context object data ba~es during method resolution, is packed into a data structure used for co~mlln;cation in the network (step 1595) and the invoker software component 1236 then transmits the packed and processed method invocation request to the dispatcher software component 1332. The processes of the dispatcher software component 1332 will be described below with reference to Figures 18A and 18B.
After the dispatcher software component 1332 completes its processing and transmits a packed response, the invoker software component 1236 receives the packed response (step 1597), unpacks the response (step 1598), and returns the re~ponse to the client application 1220 to complete its proaessing (step 1599).
If in the earlier determination (step 1583 in Figure 15C), the running method server was found not to be available, the invoker software component 1236 determines whether the server registration facility 1420 indicated any other rllnn;ng method servers capable of performing the method identified by the resolved method (~tep 1584). If so, then the retrieved information is compared to the server node table in the context object data base 630 and a QueryServer call is made to control server software component 1334 (step 1581).
Otherwise, the invoker software component seleats the server node with the highest priority from the server node table (step 1586). The control server software component 1334 of that selected server platform is then contacted using the StartServer call which indicates to the control server software component 1334 to attempt to start the approprlate application which corresponds to the method identified by the resolved method (step 1587).
After the control server software component 1334 has completed its processing and transmitted a message, the invoker software component 1236 receives the transmitted message which it then unpacks (step 1588).
If the application was started and became a method ~erver (step 1589), then the invoker software component 1236 completes itB proceBses which have already been described (step 1593 of Figure 15D). If the application was not started (step 1589), then the invoker software component 1236 asks whether there are any more nodes in the server node table of the context object data bases 630 (step 1590). If not, then an error message is generated indicating that the method invocation was unsuccessful because a server platform could not be located (step 1592), and that error message is returned to the client application 1220 (step 1599 in Figure 15D).
If, however, there are other nodes on the server node table (step 1590 in Figure 15C) then the platform with the next highest priority is selected (step 1591) and the processing of the invoker software component 1236 returns to step 1587 of Figure 15C. The loop consi8ting of steps 1587, 1588, 1589, 1590, and 1591 wlll be performed until the method server is started (step 1589) or until there are no more platforms on the server platfor~ lists (step 1590).
(3) Control Server OPeration Figures 17A and 17B show the control server procedure 1700 which represents the operations of the control server software component 1334. Persons skilled in the art will recognize many other ways of implementing the functions of control server software component 1334.
After beg;nn~ng the control server procedure 1700 in step 1702 of Figure 17A, the control server software component 1334 receives a control server message (step 1705). In response, the control server software component 1334 determines whether the control server message indicates that an application rl-nn;ng on a common platform with the control server software component 1334 requests to be registered as a method server to handle method invocation requests (step 1710). If the answer is "yes" then the control server software component 1334 registers the ~erver application as a method server by recording the necessary information about the server application with the control server registry 1425 to indicate that the method server is available. Control server software component 1334 also notifies the server registration facility 1420 to indicate that the method server ig rllnn;ng (step 1715). The running and available method server may also execute appropriate methods. The control ~erver software component 1334 also generates a success message (step 1729) to be returned to the now registered application (step 1799 in Figure 17B).
If the control server message does not indicate that an application wi~hes to be registered (step 1710 in Figure 17A), the control server software component determines whether the control server me~sage indicates that a currently registered method server requests to be unregistered with the control server software component 1334 and server registration facility 1425 (step 1720). If BO, then the control server software component 1334 unregisters the method server by removing the information from the control server registry 1425. This indicates that the application, identified by the method server, is no longer available. Control server software component 1334 also notifies the server regi~tration facility 1420 to remove the information stored in network-wide memory 704 (8tep 1725). The control 8erver 80ftware component 1334 then generates a success message (step 1729) to be returned to the now-unregistered application (step 1799 in Figure 17B).
If the control server message does not indicate that an application has requested to register or unregi8ter itself, the control server software component determines whether the control server message indicates that the invoker software component 1236 wishes to signal an asynchronous method server to expect to be invoked to execute a processed method invocation request (step 1730). If this is the case, the control server software component 1334 executes a process that signals the asynchronous method server (step 1735) and completes processing (step 1799 in Figure 17B).
As explained above, the preferred implementation of this invention can operate both with applications written to take advantage of the features of this invention, or previously written applications that have been modified for use with the preferred implementation. In 80 writing or modifying asynchronous applications to operate with the preferred implementation, a user includes program code that, in part, recognizes these asynchronous signals and, as described below, registers these signals and the following processed method invocation requests in queue. These operations are described below with reference to the processes performed by the dispatcher software component 1332.
If no other function has been requested, the control server software component 1334 determines whether the control server message indicates that the invoker software component 1236 is requesting that a new application, which resides on the Rame platform a~ the control server software component 1334, should be started to become a method server to process a method (~tep 1740 in Figure 17B). If 80, then the control server software component 1334 checks the control server regi~try 1425 (step 1745) to determine whether the method executable of the new application, corresponding to the resolved method, resides on the selected platform (step 1750).
Control server registry 1425 has a local scope 80 that only the server platform 1300 is aware of resident method executables. The registration of method executables in regi~try 1425 involves registration of the actual executable code in executable files, for example shell scripts, that implement a method, and the status of those method executables. These items preferably have only a local registration ~cope becau~e it i~ not necessary to manage the executable code globally.
If the correspo~;ng method executable is identified in the control server registry 1425, then the selected platform can be a server platform. The control 8erver software component 1334 executes a process to start the corresponding method executable and registers the resulting method server with the server registration facility 1420 and with the control server registry 1425 to indicate that the newly etarted method server i~ both r--nn;ng and available (step 1752). During this starting process, the control ~erver software component 1334 also creates a context ob~ect data base capable of being used by the started method server. Next the control server software component 1334 then generates a message indicating that the application corresponding to the resolved method has been started and is now a method server (step 1754). This message is then transmitted to the invoker software component 1236 that requested that the method server be started (step 1790), and the control server software component 1334 has completed its processing (step 1799).
If the method executable corresponding to the resolved method is not identified in the control server registry 1425, then the control server software component 1334 generates an appropriate message indicating that the method executable was not started (step 1756). This message is then transmitted to the invoker software component 1236 that requested that the method server be started (step 1790), and the control server software component 1334 has completed its processing (step 1799).
If no other function has been requested, the control server software component 1334 determines whether the control server message is a request from the invoker software component 1236 for information concerning the availability of a running method server to execute a method identified by the resolved method (step 1760). If not, the control server software component 1334 generates an error message (step 1780), transmits that message to the invoker software component 1236 (step 1790), and completes its processing (step 1799).
Otherwise the control server software component 1334 retrie~ the reque8ted information on the r~nn;ng method server from the control server registry 1425 (step 1765). If the information from the control server registry 1425 indicates that the method server identified by the resolved method is available (step 1770), then the control server software component 1334 generates a message indicating the method server' 8 availability (step 1775). This message is then transmitted to the invoker software component 1236 (step 1790), and the processing of the control server software component is complete (step 1799).
If, however, the control server regi~try 1425 indicates that the method server i8 not available (step 1770), then the control server software component 1334 generates a message indicating the unavailability of the method server (step 1777). The control server software component 1334 then transmits the generated message to the invoker software component (step 1790), and the processing of the control server software component 1334 is complete (step 1799).
(4) Dispatcher Operation The process of dispatching method servers consists of dispatching methods to be processed by method servers and transport level communications. The dispatcher software component 1332 also handles different types of method lnvocation~.
Asynchronous method invocations do not require that the client application wait for the identified method 8erver to complete processing. For example, the invocation reque8t can be placed on a queue to be performed, and the RPC
transport level call can return to the invoker software component 1334 and allow the client application to continue its own processing without being "blocked" or prevented from continuing. The queue of processed method invocation requests received from invoker software components i8 then examined by dispatcher software component 1332, such as in a dispatcher procedure 1800 of Figure 18, and performed according to a predetermined order.
Asynchronous method invocations may be requested if the cllent application does not expect to receive back a response from the method server. The only response will be an indication of whether the method invocation was successfully received by an ACAS software component on a server platform.
The response does not indicate whether the execution was successful, and will not contain any outputs of the actual method invocation, as it could for synchronous method invocations.
Synchronous method invocations are the default mode for all method invocations. With synchronous method invocations the client application that invoked the method awaits a response before continuing its own processing.
Figures 18A and 18B are a flow diagram of procedures performed or called by the dispatcher software component 1332 of Figures 12 and 14. The dispatcher procedure 1800 represents the steps 1385, 1390, and 1395 (Figure 13) performed by the dispatcher software component 1332.
Prior to entering the dispatcher procedure 1800, the dispatcher software component 1332 is in a "wait" state waiting for a processed method invocation request from an invoker software component in the network. After beg; nn;ng the dispatcher procedure 1800 (step 1802), the dispatcher software component 1332 receives a transport data structure, via the network tran~port ~ervice. This transport data structure represent~ a packed and processed method invocation request transmitted by an invoker software component in the network (step 1805). After receiving this transport data structure, the dispatcher software component 1332 unpacks and translates the transport data structure into a data structure recognizable by the server platform (step 1810). The dispatcher software component 1332 then updates a context object data base associated with the rl~nn;ng method server (step 1815). A context object data base may become associated with the rllnn;ng method server either by being created by the control server software component 1334 when starting the method server or by a user logg~ng onto the server platform and starting the method server.
The dispatcher software component 1332 next aQks whether the proceed method invocation request it received is an asynchronous invocation request to be processed by an asynchronous method server (step 1820). If not, then the dispatcher software component 1332 asks whether the invocation request includes the identification of a valid method, which in a method that can be processed by the method server (step 1825). If not, then an error message is generated (step 1840), which is then packed as a response (step 1890 in Figure 18B) and transmitted to the invoker software component (step 1895) before completing the dispatcher processing (step 1899).

If the invocation request included the identification of a valid method (step 1825 in ~igure 18A), then the dispatcher software component 1332 dispatches the valid method identified by the received invocation reguest to be executed by the method server (step 1830). If an error occurred during the execution of the valid method by the method server (step 1835), the dispatcher software component 1332 generates an appropriate error message (step 1840). The dispatcher software component 1332 then packs the error message as a response (step 1890 in Figure 18B) and transite the packed error mes~age to the invoker software component (step 1895) before completing the dispatcher processing (step 1899).
If no execution error occurred (step 1835 in Figure 18A), then the dispatcher software component 1332 packs a response (step 1890 in Figure 18B), which in this case is the processed method invocation request including any output from the method server that processed the method identified by the resolved method (step 1560 of Figure 15A). After the response is packed, it i8 transmitted to the invoker software component that originally sent the original processed method invocation request (step 1895), and the dispatcher processing is completed (step 1899 ).
If the processed method invocation reque~t received by the dispatcher software component is an asynchronous invocation request (step 1820 in Figure 18A), then the asynchronous invocation request is preferably placed on a queue to be dispatched by the dispatcher software component ~ 68061-175 1332 to be later processed as a method server (step 1850). A
message indicating the success of the asynchronous invocation request is generated (step 1855), packed as a response to the received processed method invocation request (step 1860), and then tran mitted to the invoker software component that originally sent the processed method invocation request (step 1865).
In the preferred implementation, asynchronous method servers execute asynchronous method invocation reque~ts in the order they are first placed on a queue. In executing the asynchronous requests, the dispatcher software component 1332 asks whether there are any method invocation requests on the queue to be processed by the asynchronous method server (step 1870 in Figure 18B). If there are no method invocation requests on the queue (step 1870), then the dispatcher processing is complete (step 1899).
If there were asynchronous method invocation requests on the queue (step 1870), the dispatcher software component 1332 takes the next asynchronous method invocation request off of the queue (step 1875). If the request taken off of the queue is invalid (step 1880), such as a request that cannot be processed by the method server, then processing returns to find out whether there are other queued method invocation requests (step 1870).
If the request taken of the queue is valid (step 1880), then the dispatcher software component 1332 dispatches the a~ynchronous method invocation request taken off the queue to be processed by the asynchronous method server (step 1885).

....

The question is then asked whether an error occurred in the processing of the method server (step 1887). The error, if any, is recorded (step 1888) then, or if an error did not occur, the dispatcher software component 11332 checks the queue (step 1870). In this manner all asynchronous invocation requests on the queue are processed, in turn, without blocking the client application that originated the method invocation request.
I. Summary The present invention thus provides an efficient and simple manner for an application on one platform to invoke an application on the same or a different platform without needing to know details about the other platform, or even about the other application. Such invocation can even take place between unlike platforms in a heterogeneous network.
Because, in accordance with the object-oriented techniques of this invention, the data (or instances) and application~ are not managed, those data and application~ can be managed in the manner chosen by the application developers.
By managing only objects and references to applications instead, the requirements on system resources are reduced, and the flexibility of the system is increased.
Persons of ordinary skill will recognize that modifications and variations may be made to this invention without departing from the spirit and scope of the general inventive concept. This invention in its broader aspects is therefore not limited to the ~pecific details or representative methods shown and described.

Claims (8)

1. In a data processing network which includes:
a plurality of applications capable of performing operations on instances and capable of sending and receiving messages including identifiers for instance and types of operations;
a plurality of instances corresponding to each of said applications, and a plurality of platforms operating under the control of operating systems for executing said applications;
a system for organizing communication among said applications in an object-oriented manner comprising:
memory in the network containing a data base, said data base including:
a plurality of method entries, each of said method entries corresponding to one of said applications and containing a reference to a means external to the data base for invoking a procedure to allow that application to perform a specified operation on a specified instance, a plurality of non-redundant class entries, each of said class entries containing information about a class consisting of one or more instances which share common characteristics and further containing an identification on one or more message entries, and a plurality of message entries, each of said message entries specifying information about the types of operations which may be performed on selected instances and further containing a reference to one or more method entries, the message entries identified in each class entry containing information about the types of operations which can be performed on instances associated with said class entry, and the method entries identified in each message entry containing information relating to applications capable of performing the types of operations specified in said message entry;
database control means coupled to the memory in the network, including:
means, responsive to a message from a client application, for selecting the class entries and message entries associated with the instance and type of operation identified in said message, means for selecting a method entry referenced in the selected message entry and corresponding to the requested application, means for selecting a platform capable of executing the requested application, and means for transmitting the identifier for the instance and the reference to a procedure contained in the selected platform; and, an object definition facility coupled to the memory in the network, wherein the data base includes a global class portion which is accessible throughout the network and local portions which are each accessible to only a portion of the network, wherein the data base control means includes means for searching the local data bases in a predetermined order before searching the global class data base, and wherein the object definition facility includes means for generating globally unique identifiers for types of operations and instances.

2. The system of claim 1 wherein method entries are referenced in each of the message entries by means of a method map.

3. The system of claim 1 wherein each of the method entries includes a list of attribute values describing the corresponding application.

4. The system of claim 1 wherein the class entries or method entries are hierarchically ordered into superclasses and subclasses such that the ones of the class entries or method entries which represent subclasses of a corresponding superclass inherit the information about the corresponding superclass.

5. In a data processing network which includes:
a plurality of applications capable of performing operations on instances and capable of sending and receiving messages including identifiers for instance and types of operations;
a plurality of instances corresponding to each of said applications, and a plurality of platforms operating under the control of operating systems for executing said applications;
a system for organizing communication among said applications in an object-oriented manner; and memory in the network containing a data base;
a method of modifying the data base, said method comprising the steps of:
making a plurality of method entries, each of said method entries corresponding to one of said applications and containing a reference to a means external to the data base for invoking a procedure to allow that application to perform a specified operation on a specified instance, making a plurality of non-redundant class entries, each of said class entries containing information about a class consisting of one or more instances which share common characteristics and further containing an identification on one or more message entries, and making a plurality of message entries, each of said message entries specifying information about the types of operations which may be performed on selected instances and further containing a reference to one or more method entries, the message entries identified in each class entry containing information about the types of operations which can be performed on instances associated with said class entry, and the method entries identified in each message entry containing information relating to applications capable of performing the types of operations specified in said message entry;
controlling by data base control means coupled to the memory in the network, said controlling including the steps of:
selecting, responsive to a message from a client application, the class entries and message entries associated with the instance and type of operation identified in said message, selecting a method entry referenced in the selected message entry and corresponding to the requested application, means for selecting a platform capable of executing the requested application, and transmitting the identifier for the instance and the reference to a procedure contained in the selected platform; and, coupling an object definition facility to the memory in the network, wherein the data base includes a global class portion which is accessible throughout the network and local portions which are each accessible to only a portion of the network, wherein the data base control means includes means for searching the local data bases in a predetermined order before searching the global class data base, and wherein the object definition facility includes means for generating globally unique identifiers for types of operations and instances.

6. The method of claim 1 including referencing method entries in each of the message entries by means of a method map.

7. The method of claim 1 including listing for each of the method entries, attribute values describing the corresponding application.

8. The method of claim 1 including ordering the class entries or method entries hierarchically into superclasses and subclasses such that the ones of the class entries or method entries which represent subclasses of a corresponding superclass inherit the information about the corresponding superclass.