Extending object-oriented databases with rules

Rules have been adopted as a means of expressing knowledge which is uniform throughout the type lattice but needs to be customized for each object type with integrity constraints. More specifically, such knowledge involves associations between instances, between objects, and between objects in different databases; grouping of instances; creation and deletion of object instances; and any other activity that requires a uniform approach in order to ensure consistency and transparency. A logical query language based on the representation of associations between objects, which can be made by rules, has been used. The goal was not a full-fledged object-oriented programming language, but a logical query language with base predicate associations between objects. A logical query language has the obvious advantage of expressiveness and simplicity but poses certain difficulties in evaluation; evaluation is an issue in the case of recursive queries due to time-consuming join operations. This problem was overcome by transforming recursion into iterative navigation through associations between object instances