[31] SKELETONS AND IMPLEMENTATION OBJECTS
(Part of the CORBA FAQ, Copyright © 1996)

[31.1] HOW DOES A CORBA OBJECT PROVIDE ITS SERVICES?

[Recently created (7/1997). Click here to go to the next FAQ in the “chain” of recent changes]

A CORBA Object provides a set of services to its object references. In addition to the ORB and BOA, the CORBA Object requires two additional entities in order to respond to requests. First, something must listen for requests, next something must perform the operation, and third, something must issue the proper response based upon the results of the operation. These tasks are performed by the skeleton and the object implementation. Conceptually, the implementation object provides the actual operation “know-how” and the skeleton provides the networking “know-how”. The skeleton and implementation, combine with the ORB and the BOA to support the full behavior of the particular CORBA Object.

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[31.2] HOW ARE THE SKELETON AND IMPLEMENTATION OBJECT COMBINED?

[Recently created (7/1997). Click here to go to the next FAQ in the “chain” of recent changes]

1. Derived: In the derived approach, the implementation object “is” also a skeleton. This is usually obtained via inheritance. The ORB’s IDL compiler would generate an appropriate skeleton class (based on the IDL interface and data types) and the developer would derive their own implementation class from it. The skeleton is able to listen to the network, de-marshall/re-marshall data types, etc. The implementation knows how and what to do within the body of the CORBA operations. A CORBA server will simply instantiate the implementation and tell the BOA that it “is ready”. Since the implementation “is” also a skeleton, the CORBA Object will be able to respond to CORBA requests.
2. Delegated: In the delegated approach, The ORB’s IDL compiler would generate an appropriate skeleton class (based on the IDL interface and data types) which would then delegate the actual operation execution to another class. The skeleton is still responsible for reading and writing to the network, de-marshall/re-marshall data types, etc. The implementation knows how and what to do within the body of the CORBA operations. While the implementation does not actually inherit from the skeleton, it still needs to implement the same set of minimal methods corresponding the to IDL operations. A CORBA server will need to instantiate the skeleton, instantiate the implementation, instruct the skeleton as to the where abouts of the implementation (often known as TIEing the skeleton and implementation together) and the tell the BOA that the skeleton “is ready”.

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