A framework for extending the capabilities of an event processing system using one or more plug-in components referred to herein as data cartridges. Generally speaking, a data cartridge is a self-contained unit of data that can be registered with an event processing system and can store information pertaining to one or more objects (referred to herein as extensible objects) that are not natively supported by the system. Examples of such extensible objects can include data types, functions, indexes, data sources, and others. By interacting with a data cartridge, an event processing system can compile and execute queries that reference extensible objects defined in the data cartridge, thereby extending the system beyond its native capabilities.