An information retrieval system incorporates an extensible query architecture allowing an applications programmer to integrate new query models into the system as desired. The query architecture is based on an abstract base class of query nodes, or code objects that retrieve records from the database. Specific subclasses for particular query models are derived from the base class. Each query node class includes a search function that iteratively searches the database for matching records. Query node objects are instantiated by associated node creator class objects. A parser is used to parse a search query into its components, including nested search queries used to combine various query models. The parser determines the particular search operator keywords, and the node creator object for instantiating the appropriate query node object for each search operator. The node creator objects return pointers to the created query nodes, allowing the parser to assemble complex hierarchical query nodes that combine multiple query models.