DATABASE QUERY SYSTEM

A database query system includes a query assistant that permits the user to enter only queries that are both syntactically and semantically valid (and that can be processed by an SQL generator to produce semantically valid SQL). Through the use of dialog boxes, a user enters a query in an intermediate English-like language which is easily understood by the user. A query expert system monitors the query as it is being built, and using information about the structure of the database, it prevents the user from building semantically incorrect queries by disallowing choices in the dialog boxes which would create incorrect queries. An SQL generator is also provided which uses a set of transformations and pattern substitutions to convert the intermediate language into a syntactically and semantically correct SQL query. The intermediate language can represent complex SQL queries while at the same time being easy to understand. The intermediate language is also designed to be easily converted into SQL queries. In addition to the query assistant and the SQL generator, an administrative facility is provided which allows an administrator to add a conceptual layer to the underlying database making it easier for the user to query the database. This conceptual layer may contain alternate names for columns and tables, paths specifying standard and complex joins, definitions for virtual tables and columns, and limitations on user access.