An information server may function as a centralized query broker that accepts queries from query clients, dispatches queries to potentially disparate data sources, and returns query results to query clients. An information server may centralize information access and security/control operations and may provide a set of uniform interfaces for accessing various types of data sources. A pluggable data source interface may be used for extending the data and actions that are available to an information server. The queries that arrive at the data sources are typically simple queries, which contain no sub-query addressing to a different data source. To make a data source pluggable, a data source may expose a standard interface and may store information about the data source's existence so that an information server will be able to determine, from the stored information, which data sources are available for responding to queries in the information server system.