Capturing model-based ontology evolution at the instance level: The case of DL-Lite

Abstract

Evolution of Knowledge Bases (KBs) expressed in Description Logics (DLs) has gained a lot of attention lately. Recent studies on the topic have mostly focused on so-called model-based approaches (MBAs), where the evolution of a KB results in a set of models. For KBs expressed in tractable DLs, such as those of the DL-Lite family, which we consider here, it has been shown that one faces inexpressibility of evolution, i.e., the result of evolution of a DL-Lite KB in general cannot be expressed in DL-Lite, in other words, DL-Lite is not closed under evolution. What is still missing in these studies is a thorough understanding of various important aspects of the evolution problem for DL-Lite KBs: Which fragments of DL-Lite are closed under evolution? What causes the inexpressibility? Can one approximate evolution in DL-Lite, and if yes, how? This work provides some understanding of these issues for an important class of MBAs, which cover the cases of both update and revision. We describe what causes inexpressibility, and we propose techniques (based on what we call prototypes) that help to approximate evolution under the well-known approach by Winslett, which is inexpressible in DL-Lite. We also identify a fragment of DL-Lite closed under evolution, and for this fragment we provide polynomial-time algorithms to compute or approximate evolution results for various MBAs.