Specifying dynamic and deontic integrity constraints

摘要

In the dominant view of knowledge bases (KB's), a KB is a set of facts (atomic sentences) and integrity constraints (IC's). An IC is then a sentence which must at least be consistent with the other sentences in the KB, This view obliterates the distinction between, for example, the constraint that age is a natural number (which is true of the universe of discourse (UoD) but may be false in a particular implementation of a KB), and the constraint that a class must have precisely one teacher (which is false of the UoD if a class actually has two teachers). The second constraint is called deontic and constrains the UoD; the first constraint is a necessary truth of the UoD and does not constrain the UoD. Instead, it constrains the implementation of the KB. We argue that the distinction between necessary and deontic IC's is relevant for KB modeling and that it imposes a more complicated modeling discipline on the KB designer than hitherto realized. We show that both types of constraints can be specified in the single framework provided by a deontic variant of dynamic logic, which has the added advantage of being able to specify dynamic constraints as well. We give a simple example to illustrate the difference between dynamic and static specification of deontic IC's, and a non-trivial example of a KB specification with static, dynamic and deontic constraints.