The Semantic Web Explained

Transcription

1 The Semantic Web Explained The Semantic Web is a new area of research and development in the field of computer science, aimed at making it easier for computers to process the huge amount of information on the web, and indeed other large databases, by enabling them not only to read but also to understand the information. Based on successful courses taught by the authors, and liberally sprinkled with examples and exercises, this comprehensive textbook describes not only the theoretical issues underlying the Semantic Web, but also algorithms, optimisation ideas and implementation details. The book will therefore be valuable to practitioners as well as students, indeed to anyone who is interested in Internet technology, knowledge engineering or description logics. Supplementary materials available online include the source code of program examples and solutions to selected exercises. Péter Szeredi is a Professor at the Budapest University of Technology and Economics (BUTE). In the mid 1970s he authored the first Hungarian Prolog interpreter and led the development of the MProlog system, a pioneering Hungarian software product sold worldwide in the 1980s. His main fields of interest include: declarative programming (logic programming, constraint programming, the Prolog language); semantic technologies (Semantic Web, semantic integration); exploiting parallelism and programming languages supporting parallelism; as well as the implementation of programming languages. He is the author and co-author of about 90 peer-reviewed publications, including 14 books or book chapters and eight journal publications. In recognition of his pioneering work in the field, he was honoured by the Association of Logic Programming as one of the 15 Founders of Logic Programming. Gergely Lukácsy is a Software Architect at Cisco Systems, Ireland. He received his Ph.D. in Computer Science from the Budapest University of Technology, Hungary, in June The main contribution in his Ph.D. dissertation was a novel description logic reasoning approach that works effectively in cases when there are huge amounts of data. This result is particularly important for the Semantic Web area, where it is essential to have systems that can reason efficiently over large data sets. Dr Lukácsy has published more than 25 articles in journals, books, refereed conference proceedings and workshops. He has been working on various research projects involving semantic technologies and logic programming since His main results include the DLog reasoner, which uses logic programming techniques for efficient reasoning, including program analysis and transformation techniques and parallelisation. He has also been involved in the design and development of logic-based information integration systems that use knowledge representation, constraint logic programming and reasoning techniques. Tamás Benkő is a Research Associate at the Digital Enterprise Research Institute, Ireland. He is involved in the development of the Semantic Web indexing project Sindice. His main fields of interest include declarative programming (logic programming, constraint programming, the Prolog language) and semantic technologies (Semantic Web, semantic integration). He is the author or co-author of several related conference papers and books.

2 The Semantic Web Explained

3 The Semantic Web Explained The Technology and Mathematics behind Web 3.0 PÉTER SZEREDI Budapest University of Technology and Economics (BUTE) GERGELY LUKÁCSY Cisco Systems, Ireland TAMÁS BENKŐ Digital Enterprise Research Institute, Ireland With contributions by ZSOLT NAGY

4 University Printing House, Cambridge CB2 8BS, United Kingdom Cambridge University Press is part of the University of Cambridge. It furthers the University s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. Information on this title: / Originally published in Hungarian as A Szemantikus Világháló Elmélete És Gyakorlata by Typotex, 2005 Szeredi Péter, Lukácsy Gergely, Benkő Tamás, Nagy Zsolt, Typotex, 2005 First published in English by Cambridge University Press 2014 English translation Cambridge University Press 2014 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. Printed in the United Kingdom by Clays, St lves plc A catalogue record for this publication is available from the British Library Library of Congress Cataloguing in Publication data Szeredi, Péter, 1949 author. [Szemantikus világháló elmélete és gyakorlata. English] The Semantic Web explained : the technology and mathematics behind Web 3.0 / Péter Szeredi, Budapest University of Technology and Economics (BUTE), Gergely Lukácsy, Cisco Systems, Ireland, Tamás Benkő, Digital Enterprise Research Institute, Ireland ; with contributions by Zsolt Nagy. pages cm ISBN (paperback) 1. Semantic Web. I. Lukácsy, Gergely, author. II. Benkő, Tamás, author. III. Title. TK S dc ISBN Paperback Additional resources for this publication are at Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate.

5 Contents Introduction page 1 Part I The Semantic Web 7 1. The World Wide Web today The architecture of the web Conventional web search engines Problems with searching the web Possible solutions Summary The Semantic Web and the RDF language Introduction The XML language The basics of the RDF language The XML syntax for RDF Special RDF constructs Representing background knowledge: RDF schema Examples of RDF use Summary Managing and querying RDF sources RDF descriptions on the web Parsing and processing metadata Querying RDF sources Reasoning during the execution of queries Optimising RDF queries Summary 168

6 vi CONTENTS Part II Ontologies and logics Description Logic Introduction An informal introduction to the DL formalism The AL DL language The AL language family The SHIQ language family Terminological reasoning tasks Eliminating terminological axioms ABoxes Mapping DL languages to first-order logic Advanced DL languages Summary Reasoning on simple DL languages Reasoning in the AL language The ALCN tableau algorithm an introduction The ALCN tableau algorithm for empty TBoxes The ALCN tableau algorithm for non-empty TBoxes Handling ABoxes in the ALCN tableau algorithm Summary Implementing a simple DL reasoning engine Introduction Executing the reasoning engine Data structures Transforming concepts to negation normal form The entry point of the tableau algorithm Tableau transformation rules Blocking Auxiliary functions Challenges Summary The SHIQ tableau algorithm An outline of the SHIQ tableau algorithm Transitive roles; the language S Role hierarchies extension H Inverse roles extension I Functional restrictions extension F Qualified number restrictions extension Q The complete SHIQ tableau algorithm The SHIQ tableau algorithm for ABoxes 385

7 CONTENTS vii 7.9. Optimisation of the tableau algorithm Summary 404 Part III Ontologies and the Semantic Web The Web Ontology Language The language OWL an introduction The ontology language OWL Revision of the OWL language: OWL Summary 450 References 451 Index 460