Object Knowledge Base Revision

A revision framework for object-based knowledge representation languages is presented. It is defined by adapting logical revision to objects and characterised both semantically and syntactically. The syntactic analysis of revision shows that it can be easily interpreted in terms of object structures (e.g. moving classes or enlarging domains). This is the source of the implementation and it enables users to be involved in the revision process. There has been comprehensive work done on revision in logical formalisms. However, due to several factors (complexity of revision and decision procedures, needs not well-stated [7] and mismatch between logical formalisms and implemented knowledge representation systems), little have been implemented. Moreover, very few studies (with the notable exception of [11]) have been devoted to revision in object formalisms. The present work attempts to transfer the results of logical revision to the field of object-based knowledge representation systems. Moreover, its goal is to come up with an implemented system in the context of error correction during knowledge base editing. Two noticeable points are thus taken into account: • the revision must take advantage of the structure of object formalisms (the developed operator is grounded on a language which enables a localised syntactic characterisation of inconsistency and a natural interpretation of minimal revisions in terms of objects); • the user can be interactively asked about the possible revisions. The paper begins by formalising a basic object-based language (§1) in order to formally characterise the kind of revision which is being performed. Then we introduce a syntactic manipulation of the knowledge bases required in order to transpose usual revision notions such as contraction and minimality (§2). In section 3, revision is defined and minimality criterion is introduced. They are found to closely follow the object-based structure. In the last section, we finally present the implementation of revision and its embedding in an actual knowledge representation system. Proof of propositions, extensions and extensive examples can be found in [3]. 1. OBJECT REPRESENTATION LANGUAGE The definition of a language corresponding to object-based notions has two purposes: formally defining what objects mean and allowing an easier transposition from logical revision to object models. Although the language presented here might seem simple, it covers in fact a large part of object representation systems.