10.6.1 Basics

The idea is to get a behavior similar to assert/1, retract/1 and clause/2, but the terms are stored on files instead of in primary memory.

The differences compared with the Prolog database are:

• A database must be opened before any access and closed after the last access. (There are special predicates for this: db_open/[4,5] and db_close/1.)
• The functors and the indexing specifications of the terms to be stored have to be given when the database is created. (see The DB-Spec).
• The indexing is specified when the database is created. It is possible to index on other parts of the term than just the functor and first argument.
• Changes affect the database immediately.
• The database will store variables with attributes or with blocked goals as ordinary variables.

Some commercial databases can’t store non-ground terms or more than one instance of a term. This library module can however store terms of either kind.