Object Interconnections Developing C + + Servant Classes Using the Portable Object Adapter

This is the third column in our series explaining the new OMG Portable Object Adapter. An Object Adapter is the CORBA component responsible for adapting CORBA’s concept of objects to a programming language’s concept of servants. As you’ll recall from previous columns [1, 2], CORBA objects are “abstract” entities defined by IDL interfaces. Likewise, servants are “concrete” implementations of CORBA objects written in a particular programming language, such as C++ or Java. The Portable Object Adapter (POA) [3] is a replacement for the Basic Object Adapter (BOA) defined in earlier CORBA specifications. The newest version of CORBA, CORBA 2.2, [4], contains both the POA specification and the BOA specification. The BOA specification will be removed in future versions of CORBA, however, because the POA specification supersedes the BOA. As POA implementations are provided by vendors, therefore, C++ developers creating new CORBA applications should use the POA to satisfy the object adapter requirements of their servers. The examples we showed in the previous column showed how to obtain object references from servants, as well as how to register servants with a POA instance. However, we did not show the definitions of the C++ servant classes. In addition to addressing this omission, this column explains how the new POA specification separates the client-side stub hierarchy from the server-side skeleton hierarchy in order to facilitate collocation and ensure source-level portability.