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2.7 OpenDoc Object Model

 


                                              



 
   Figure 37. OpenDoc Object Management Services - System Object Model 

   If objects are to be assembled they must be compatible with one another. 
   This is rarely a problem when writing a single program, because all the 
   objects are written in the same language, run on the same machine, and use 
   the same operating system. But building entire information systems out of 
   objects is quite a different matter. Objects have to interact with each 
   other even if they are written in different languages, and run on 
   different hardware and software platforms. 

   David Taylor, Business Engineering with Object Technology 

   This chapter describes the basic architecture of the object model used by 
   OpenDoc.  SOM System Object Model provides the underlying object model for 
   OpenDoc components. 

   SOM is the IBM implementation of the CORBA standard.  CORBA stands for 
   Common Object Request Broker Architecture, which is defined by a 
   standardization group called Object Management Group.  This group is 
   defining standards necessary for objects to interoperate.  CORBA defines a 
   standard way of objects to communicate. 

   A component is an encapsulated building block which must be able to be 
   plugged in and out at run time.  Components, or parts as they are called 
   in OpenDoc, can be developed independently by ISVs without knowing 
   anything from the other components.  Object technology is a great 
   philosophy to provide the necessary encapsulation to minimize the 
   dependencies of components to the outside world.  Part of the object 
   technology paradigm is to separate the definition of a component interface 
   from the implementation.  A component technology must have a standardized 
   way of defining and describing interfaces and it must provide methods for 
   other components to discover their interfaces dynamically. 

   Therefore an object model must provide the following: 

   1.  A standardized binary application interface to enable dynamic loading 
       and replacing of components very similar to the way DLLs are working. 

   2.  An interface repository, which is available at run time to all 
       components.  It provides the information and the methods to discover 
       the interfaces from other parts and objects at run time. 

   3.  A standardized way to describe the interfaces. 


   There is a standard addressing all these requirements and defining all of 
   the infrastructure necessary for such a component technology.  It was 
   defined by the Object Management Group. 

Subtopics:

   2.7.1 The Object Management Architecture
   2.7.2 Common Facilities
   2.7.3 SOM
   2.7.4 Distributed SOM
   2.7.5 SOM and OpenDoc
   2.7.6 Differences between SOM and COM
   2.7.7 OpenDoc and SOM Summary and Outlook

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