The dynamics of belief and knowledge is one of the major components of any autonomous system that should be able to incorporate new pieces of information. We show that knowledge base dynamics has interesting connection with kernel change via hitting set and abduction. The approach extends and integrates standard techniques for efficient query answering and integrity checking. The generation of hitting set is carried out through a hyper tableaux calculus and magic set that is focussed on the goal of minimality. Many different view update algorithms have been proposed in the literature to address this problem. The present paper provides a comparative study of view update algorithms in rational approach.
Furthermore, and at a first sight more related to our work, some work has been done on ontology systems and description logics (Qi and Yang @cite_35 , and Kogalovsky @cite_38 ). Finally, when we presented connection between belief update versus database update, we did not talk about complexity (see the works of Liberatore @cite_99 @cite_1 , Caroprese @cite_34 , Calvanese's @cite_11 , and Cong @cite_82 ).
@cite_99 @cite_35 @cite_38 @cite_82 @cite_1 @cite_34 @cite_11
1984302133 1521011401 2078954026 2117854600 1623257973 1496385246 2039781767
Abstract Belief revision and belief update are two different forms of belief change, and they serve different purposes. In this paper we focus on belief update, the formalization of change in beliefs due to changes in the world. The complexity of the basic update (introduced by Winslett, 1990) has been determined by Eiter and Gottlob (1992). Since then, many other formalizations have been proposed to overcome the limitations and drawbacks of Winslett's update. In this paper we analyze the complexity of the proposals presented in the literature: the standard semantics by Winslett (1986), the minimal change with exception and the minimal change with maximal disjunctive information by Zhang and Foo (1996), the update with disjunctive function by Herzig (1996), the abduction-based update and the generalized update by Boutilier (1996). We relate some of these approaches to belief update to previous work on closed world reasoning. This invention relates to elbow crutches and provides a crutch to enable a patient with leg disability to raise himself from a sitting position to a standing position. Basically the invention consists in an elbow crutch, the length of which is adjustable under the control of a manually operable lever. In particular, the crutch comprises two telescopically arranged tubular members and a spring urging one tubular member outwardly with respect to the other. A rack and pawl are provided to prevent relative movement between the two members, and the pawl is controlled by the manually operable lever. Normally a patient will use a pair of crutches in accordance with the invention, and will initially operate the lever of each crutch to reduce the length of the crutch to the minimum by pressing the crutch on the floor. He can then raise himself by supporting his weight on the two crutches alternately and operating the control lever of the crutch which is not supporting his weight to allow that crutch to extend. Studies aimed at ensuring semantic access to databases have a long history and originated at early stages of database technology development. Unfortunately, they have not led yet to the creation of widely accepted industrial technologies. In the last decade, the activity of the W3C consortium in the field of Semantic Web and development of standards of the ontology description languages induced a new activity wave in developing tools for systems of semantic access to databases and a new class of database systems, the so-called ontology-based data access (OBDA) systems. In such systems, ontology is used as a conceptual schema of the subject domain and as a basis of the user interface for SQL database systems. Approaches proposed in recent years do not ensure "final" solution of the problem. Nevertheless, ontology description languages were created that make it possible to achieve an acceptable compromise between their expressiveness, which remains sufficient for many applications, and computational complexity of reasoning on ontologies and processing queries to data stored in large databases. Prerequisites have been created for appearance of industrial technologies for development of systems of the above-specified class. In the paper, a survey of recent basic results and developments in this field is presented. This paper investigates three problems identified in [1] for annotation propagation, namely, the view side-effect, source side-effect, and annotation placement problems. Given annotations entered for a tuple or an attribute in a view, these problems ask what tuples or attributes in the source have to be annotated to produce the view annotations. As observed in [1], these problems are fundamental not only for data provenance but also for the management of view updates. For an annotation attached to a single existing tuple in a view, it has been shown that these problems are often intractable even for views defined in terms of simple SPJU queries [1]. We revisit these problems by considering several dichotomies: (1) views defined in various subclasses of SPJU, versus SPJU views under a practical key preserving condition; (2) annotations attached to existing tuples in a view versus annotations on tuples to be inserted into the view; and (3) a single-tuple annotation versus a group of annotations. We provide a complete picture of intractability and tractability for the three problems in all these settings. We show that key preserving views often simplify the propagation analysis. Indeed, some problems become tractable for certain key preserving views, as opposed to the intractability of their counterparts that are not key preserving. However, group annotations often make the analysis harder. In addition, the problems have quite diverse complexity when annotations are attached to existing tuples in a view and when they are entered for tuples to be inserted into the view. A propositional knowledge base can be seen as a compact representation of a set of models. When a knowledge base T is updated with a formula P, the resulting set of models can be represented in two ways: either by a theory T' that is equivalent to TaP or by the pair 〈T,P〉. The second representation can be super-polinomially more compact than the first. In this paper, we prove that the compactness of this representation depends on the specific semantics of a, e.g., Winslett's semantics is more compact than Ginsberg's. This paper introduces and studies a declarative framework for updating views over indefinite databases. An indefinite database is a database with null values that are represented, following the standard database approach, by a single null constant. The paper formalizes views over such databases as indefinite deductive databases, and defines for them several classes of database repairs that realize view-update requests. Most notable is the class of constrained repairs. Constrained repairs change the database "minimally" and avoid making arbitrary commitments. They narrow down the space of alternative ways to fulfill the view-update request to those that are grounded, in a certain strong sense, in the database, the view and the view-update request. View-based query answering is the problem of answering a query based only on the precomputed answers to a set of views. While this problem has been widely investigated in databases, it is largely unexplored in the context of Description Logic ontologies. Differently from traditional databases, Description Logics may express several forms of incomplete information, and this poses challenging problems in characterizing the semantics of views. In this paper, we first present a general framework for view-based query answering, where we address the above semantical problems by providing two notions of view-based query answering over ontologies, all based on the idea that the precomputed answers to views are the certain answers to the corresponding queries. We also relate such notions to privacy-aware access to ontologies. Then, we provide decidability results, algorithms, and data complexity characterizations for view-based query answering in several Description Logics, ranging from those with limited modeling capability to highly expressive ones.