One Abductive Logic Programming Procedure for Two Kinds of Updates

We distinguish schema updates and user updates. A crucial benchmark for the assimilation of new knowledge via updates is the enforcement of integrity. The procedures SLIC for integrity checking of schema updates and SLDAI for integrity maintenance of user updates are forged into the abductive procedure SLDAI*, for satisfying schema and user update requests. SLDAI* computes modifications of the extensional part of the database in order to satisfy the requests and to preserve integrity. Similar to other abductive procedures for knowledge assimilation, SLDAI* homogenizes queries and updates: Queries can be interpreted as user update requests; inferred hypotheses which justify computed answers can be interpreted as updates which satisfy the requests. Moreover, abductive consistency proofs are generalized in SLDAI* to implement hypothetical schema updates. 1 Two kinds of updates and procedures Various kinds of updates can be encountered in contemporary database systems as well as in the database research literature. In this paper, we distinguish schema updates and user updates. Schema updates means that "intensional" database clauses are requested to be inserted, deleted or modified explicitly. Insertions and deletions of clauses defining database views or integrity constraints are typical cases of schema updates. User updates means that an update request is expressed by the specification of an arbitrary closed formula which is required to become true in the updated state. View updates realized by modifications of "extensional" database clauses are a typical case of user updates. Also, various kinds of procedures for enforcing integrity constraints upon updates can be met in database systems and in the literature. For instance, in [2], a generalization of SLDNF called SLIC is discussed. SLIC checks if an update consisting of a finite set of addtions and deletions of database clauses would violate integrity. Its efficiency has compared favourably to other integrity checking procedures which preceded SLIC (cf. [1]). A shortcoming of SLIC is that its reaction to integrity violation is passive, in the sense that it simply rejects update requests that otherwise would violate integrity. In response to that, the active database procedure SLDAI has been proposed in [3]. For a given user update request, SLDAI computes modifications of the extensional database such that the request becomes satisfied and integrity remains satisfied in the updated state. However, a shortcoming of SLDAI (and also of other, comparable abductive procedures in the literature) is that it cannot readily handle schema updates. INSTITUT F UR INFORMATIK Lehrund Forschungseinheit f ur Programmierund Modellierungssprachen Oettingenstra e 67, D{80538 M unchen One Abductive Logic Programming Procedure for Two Kinds of Updates Hendrik Decker appeared in B. Freitag et al (eds), Proc. DYNAMICS'97, Port Je erson (New York) http://www.pms.informatik.uni-muenchen.de/publikationen Forschungsbericht/Research Report PMS-FB-1997-16, September 1997