In this paper, we argue that to apply rationality results of belief dynamics theory to various practical problems, it should be generalized in two respects: first of all, it should allow certain part of belief to be declared immutable; and secondly, the belief state need not be deductively closed. Such a generalization of belief dynamics, referred to as knowledge base dynamics, is presented, along with the concept of generalized contraction to contract a sentence from knowledge base. We show that knowledge base dynamics has interesting connections with abduction, thus enabling us to use abductive procedures to realize contractions. Finally, we demonstrate how knowledge base dynamics can provide an axiomatic characterization for deleting view atoms from databases.