The Clausal Data Base¶

Predicates in YAP may be dynamic or static.

By default, when consulting or reconsulting, predicates are assumed to be static: execution is faster and the code will probably use less space. Static predicates impose some restrictions: in general there can be no addition or removal of clauses for a procedure if it is being used in the current execution.

Dynamic predicates allow programmers to change the Clausal Data Base with the same flexibility as in C-Prolog. With dynamic predicates it is always possible to add or remove clauses during execution and the semantics will be the same as for C-Prolog. But the programmer should be aware of the fact that asserting or retracting are still expensive operations, and therefore he should try to avoid them whenever possible.