Abstract: Apparatus for designing a multilevel secure database management system based on a multilevel logic programming system. The apparatus includes a multilevel knowledge base which has a multilevel database in which data are classified at different security levels. The multilevel knowledge base also includes schema, which describe the data in the database, and rules, which are used to deduce new data. Also included are integrity constraints, which are constraints enforced on the data, and security constraints, which are rules that assign security levels to the data. The system further includes users cleared to the different security levels for querying the multilevel database, and a multilevel logic programming system is provided for accessing the multilevel knowledge base for processing queries and for processing the integrity and security constraints. The multilevel database management system makes deductions and gives complete answers to queries and prevents certain unauthorized inferences.