Compilation of multiple file queries in a meta-database system

A meta-database system is constructed for describing the contents of very large databases. The meta-database is implemented as data structures in a symbol manipulation language, separate from the underlying database system. A number of programs are built around the meta-database. The most important program module is a query compiler, which translates a non-procedural query language called LRL into a lower level language (COBOL). LRL permits the specification of database retrievals without stating which files are to be used in the search, or how they shall be connected. This is decided automatically by the query compiler. A major feature of the system is a method, the Focus method, for compiletime optimization of these choices. Other facilities include the definition of "views" of the database; data directory services; authority codes; and meta-database entry and update.Design issues discussed include the decision to compile rather than interpret non-procedural query languages; the decision to separate the meta-database from the underlying database system; and the problem of achieving an architecture convertible to any underlying database system. Experience with one such conversion is reported.