Normally, the definition for an operation and the definitions for the toolkit entities (data, context, formats, and services) used by the operation are in the appropriate generic toolkit definition files. In some cases, it is better store all or part of the operation definition in an XML file that is not one of generic toolkit definition files. An operation defined in this way is a self-defined operation. Using a self-defined operation is preferable when the application is running and should not be stopped and you need to add a new operation or change an existing one, when the application cannot immediately download the full set of toolkit definition files, or when the generic definition files become unwieldy due to their size. From an implementation point of view, there is no difference between a self-defined operation and an operation defined in the toolkit operation definition file. The only difference is in the distribution scheme used for the definitions of the objects the operations use.

The file for a self-defined operation can contain the operation definition itself, the operation's context definition, and the data, services, and formats that the operation requires to execute. The self-defined operations file may also contain references to entities defined in the generic toolkit definition files. The self-defined operation file cannot contain references to other self-defined operation files but it can contain more than one operation definition.