31.5.1 Conventions

The following conventions are used in the predicate descriptions below.

• Mode is either update or read or enumerate. In mode read no updates can be made. Mode enumerate is like mode read, but indexing cannot be used, i.e. you can only sequentially enumerate the items in the database. In mode enumerate only the file storing the terms along with their references is used.
• EnvRef is a reference to an open database environment. The environment is returned when it is opened. The reference becomes invalid after the environment has been closed.
• DBRef is a reference to an open database. The reference is returned when the database is opened. The reference becomes invalid after the database has been closed.
• TermRef is a reference to a term in a given database. The reference is returned when a term is stored. The reference stays valid even after the database has been closed and hence can be stored permanently as part of another term. However, if such references are stored in the database, automatic compression of the database (using db_compress/[2,3]) is not possible, in that case the user has to write her own compressing predicate.
• SpecList is a description of the indexing scheme; see The DB-Spec.
• Term is any Prolog term.
• Iterator is a non-backtrackable mutable object. It can be used to iterate through a set of terms stored in a database. The iterators are unidirectional.