Abstract: A method and system are provided for mapping between an application relational database of arbitrary structure and an application knowledge base in order to permit a user to draw inference through a knowledge base. Also included are procedures for translating knowledge base queries into database queries, for transforming data retrieved from the database into units (structured objects) in the knowledge base and for updating a relational database based on changes made to the application knowledge base. These procedures are supported by general purpose knowledge bases. The method includes providing mapping knowledge bases for storing the mapping between an arbitrary relational database and the application knowledge base. The mapping between classes in the application knowledge base and the relations on a database is stored explicitly in units in a user mapping knowledge base. These units are called class maps.