Object and class definitions written in the OS/2 operating system and prior to OS/2 operating system Version 3, were defined in IBM object interface definition language (OIDL) and placed in a class definition file, also called a CSC file. This file was then used as input to the SOM compiler to generate language binding files.

SOM was enhanced to conform with the Object Management Group's (OMG) Common Object Request Broker Architecture (CORBA**) standards. This required changing the syntax of the class definition language from IBM OIDL to CORBA's interface definition language (IDL). The bindings created by the SOM compiler were also changed to make them compatible with the CORBA standards.

Class definitions written in OIDL and residing in CSC files should be converted to IDL before being used with the SOM compiler. This conversion allows the use of multiple inheritance, exception handling, type checking, and automatic descriptor support. In addition, the programs generated from IDL class descriptions are significantly smaller and run faster than programs generated from OIDL class definitions.