Object-centered constraints

The notion of object-centered (O-C) constraints, a subset of range-restricted Horn clauses with existential variables is presented. O-C constraints correspond, intuitively, to sets of clauses that involve connected objects or objects that can be located through navigation. Other types of constraints, e.g. transition or other temporal constraints are not specifically addressed. The research philosophy adopted is that such constraints can be expressed by introducing additional constructs into the schema, e.g. old-Student or new-Student and then expressing constraints in the same manner as the O-C constraints. This approach is conceptually accurate; it provides a uniform method for expressing and enforcing constraints using generalized constraint analysis. It allows the user to precisely describe the intended semantics, e.g. when to delete the old values after an update. This philosophy basically states that database constraints necessarily constrain database objects; in order to address additional issues like old/new values, the additional structures should be brought into the purview of the database by defining them in the database schema