TLFeBOOK 1.5 Book Overview 1.5 Book Overview In this book we concentrate on the Semantic Web technologies that have reached a reasonable degree of maturity In Chapter 2 we discuss XML and related technologies. XML introduces structure to Web documents, thus supporting syntactic interoperability. The structure of a document can be made machine-accessible through DTDs and XML Schema. We also discuss namespaces; accessing and querying XML documents using XPath; and transforming XML documents with XSLT. In Chapter 3 we discuss RDF and RDF Schema. RDF is a language in which we can express statements about objects (resources); it is a standard data model for machine-processable semantics. RDF Schema offers a number of modeling primitives for organizing RDF vocabularies in typed hierarchies Chapter 4 discusses OWL, the current proposal for a Web ontology lan- guage. It offers more modeling primitives, compared to RDF Schema, and has a clean, formal semantics. pter 5 is devoted to rules, both monotonic and nonmonotonic, in th framework of the Semantic Web. While this layer has not yet been fully de- fined, the principles to be adopted are quite clear, so it makes sense to present Chapter 6 discusses several application domains and explains the benefits that they will draw from the materialization of the Semantic Web vision. Chapter 7 describes the development of ontology-based systems for the Web and contains a miniproject that employs much of the technology de- cribed in this book Finally, chapter 8 discusses briefly a few issues which are currently under debate in the Semantic Web community 1.6 Summary The Semantic Web is an initiative that aims at improving the current state of the World Wide web The key idea is the use of machine-processable Web information. Key technologies include explicit metadata, ontologies, logic and infer- encing, and intelligent agents The development of the Semantic Web proceeds in layers TLFeBOoK
1.5 Book Overview 19 1.5 Book Overview In this book we concentrate on the Semantic Web technologies that have reached a reasonable degree of maturity. In Chapter 2 we discuss XML and related technologies. XML introduces structure to Web documents, thus supporting syntactic interoperability. The structure of a document can be made machine-accessible through DTDs and XML Schema. We also discuss namespaces; accessing and querying XML documents using XPath; and transforming XML documents with XSLT. In Chapter 3 we discuss RDF and RDF Schema. RDF is a language in which we can express statements about objects (resources); it is a standard data model for machine-processable semantics. RDF Schema offers a number of modeling primitives for organizing RDF vocabularies in typed hierarchies. Chapter 4 discusses OWL, the current proposal for a Web ontology language. It offers more modeling primitives, compared to RDF Schema, and has a clean, formal semantics. Chapter 5 is devoted to rules, both monotonic and nonmonotonic, in the framework of the Semantic Web. While this layer has not yet been fully de- fined, the principles to be adopted are quite clear, so it makes sense to present them. Chapter 6 discusses several application domains and explains the benefits that they will draw from the materialization of the Semantic Web vision. Chapter 7 describes the development of ontology-based systems for the Web and contains a miniproject that employs much of the technology described in this book. Finally, chapter 8 discusses briefly a few issues which are currently under debate in the Semantic Web community. 1.6 Summary • The Semantic Web is an initiative that aims at improving the current state of the World Wide Web. • The key idea is the use of machine-processable Web information. • Key technologies include explicit metadata, ontologies, logic and inferencing, and intelligent agents. • The development of the Semantic Web proceeds in layers. TLFeBOOK TLFeBOOK
TLFeBOOK ggested Reading An excellent introductory article, from which, among others, the scenario in section 1.2.4 was adapted T Berners-Lee, J Hendler, and O. Lassila. The Semantic Web. Scientific American 284(May 2001): 34-43 An inspirational book about the history (and the future)of the Web is T. Berners-Lee, with M. Fischetti. Weaving the Web. San Francisco: Harper, Many introductory articles on the Semantic Web are available online. Here we list a few T Berners-Lee Semantic Web Road Map. September 1998 http://www.w3.org/designlssUes/semantic.htmi> T Berners-Lee. Evolvability. March 1998. <http://www.w3.org/designissues/evolution.htmi> T. Berners-Lee. What the Semantic Web Can Represent. September 1998 <http://www.w3.org/designlssues/rdfnot.htmi>. E Dumbill. The Semantic Web: A Primer. November 1, 2000 <http://www.xml.com/pub/a/2000/11/01/semanticweb/> F. van Harmelen and D. Fensel. Practical Knowledge Representation for theWeb<http://www.cs.vu.nl/frankh/postscript/i]ca199-iil.html J Hendler. Agents and the Semantic Web. IEEE Intelligent Systems 16 (March-April 2001): 30-3 Preprintat<http://www.cs.umd.edu/users/hendler/agentweb.htmi> S Palmer. The Semantic Web, Taking Form. <http://infomesh.net/2001/06/swform/> . S. Palmer. The Semantic Web: An Introduction A Swartz. The Semantic Web in breadth <http://logicerror.com/semanticweb-long> TLFeBOoK
20 1 The Semantic Web Vision Suggested Reading An excellent introductory article, from which, among others, the scenario in section 1.2.4 was adapted. • T. Berners-Lee, J. Hendler, and O. Lassila. The Semantic Web. Scientific American 284 (May 2001): 34-43. An inspirational book about the history (and the future) of the Web is • T. Berners-Lee, with M. Fischetti. Weaving the Web. San Francisco: Harper, 1999. Many introductory articles on the Semantic Web are available online. Here we list a few: • T. Berners-Lee. Semantic Web Road Map. September 1998. <http://www.w3.org/DesignIssues/Semantic.html>. • T. Berners-Lee. Evolvability. March 1998. <http://www.w3.org/DesignIssues/Evolution.html>. • T. Berners-Lee. What the Semantic Web Can Represent. September 1998. <http://www.w3.org/DesignIssues/RDFnot.html>. • E. Dumbill. The Semantic Web: A Primer. November 1, 2000. <http://www.xml.com/pub/a/2000/11/01/semanticweb/>. • F. van Harmelen and D. Fensel. Practical Knowledge Representation for the Web. <http://www.cs.vu.nl/∼frankh/postscript/IJCAI99-III.html>. • J. Hendler. Agents and the Semantic Web. IEEE Intelligent Systems 16 (March-April 2001): 30-37. Preprint at <http://www.cs.umd.edu/users/hendler/AgentWeb.html>. • S. Palmer. The Semantic Web, Taking Form. <http://infomesh.net/2001/06/swform/>. • S. Palmer. The Semantic Web: An Introduction. <http://infomesh.net/2001/Swintro/>. • A. Swartz. The Semantic Web in Breadth. <http://logicerror.com/semanticWeb-long>. TLFeBOOK TLFeBOOK
TLFeBooK 21 A Swartz and J Hendler. The Semantic Web: A Network of Content for heDigitalCity<http://blogspace.com/rdf/swartzhendler.htmB> R. Jasper and A. Tyler. The Role of Semantics and Inference in the Semar tic Web: A Commercial Challenge <http://www.semanticweb.org/swws/proGram/position/ soi-jasper.pdf> There are several courses on the semantic Web that have extensive material F van Harmelen et al. Web-Based Knowledge Representation. <http://www.cs.vu.nl/nmarta/wbkr.htmb> <http://www.cse.lehigh.edu/heflin/courses/semweb/>. A Sheth Semantic Web <http://isdiS.cs.uga.edu/semwebcourse/index.htmi> H. Boley, S. Decker, and M. Sintek. Tutorial on Knowledge Markup Tech niques.<http://www.dfki.uni-kl.de/km/knowmark/> A number of Web sites maintain up-to-date information about the Semantic Web and related topics <http://www.semanticweb.org> <http://www.ontology.org There is a good selection of research papers providing technical information on issues relating to the Semantic Web D Fensel, J Hendler, H. Lieberman and W. Wahlster, eds. Spinning the Semantic Web. Cambridge, MA: MIT Press, 200 J Davies, D. Fensel and F van Harmelen, eds. Towards the Semantic Web Ontology-Driven Knowledge Management. New York: Wiley, 2002 onference series of the International Semantic Web Conference(se TLFeBOOK
Suggested Reading 21 • A. Swartz and J. Hendler. The Semantic Web: A Network of Content for the Digital City. <http://blogspace.com/rdf/SwartzHendler.html>. • R. Jasper and A. Tyler. The Role of Semantics and Inference in the Semantic Web: A Commercial Challenge. <http://www.semanticweb.org/SWWS/program/position/ soi-jasper.pdf>. There are several courses on the Semantic Web that have extensive material online: • F. van Harmelen et al. Web-Based Knowledge Representation. <http://www.cs.vu.nl/∼marta/wbkr.html>. • J. Heflin. The Semantic Web. <http://www.cse.lehigh.edu/∼heflin/courses/semweb/>. • A. Sheth. Semantic Web. <http://lsdis.cs.uga.edu/SemWebCourse/index.html>. • H. Boley, S. Decker, and M. Sintek. Tutorial on Knowledge Markup Techniques. <http://www.dfki.uni-kl.de/km/knowmark/>. A number of Web sites maintain up-to-date information about the Semantic Web and related topics: • <http://www.SemanticWeb.org>. • <http://www.w3.org/2001/sw/>. • <http://www.ontology.org>. There is a good selection of research papers providing technical information on issues relating to the Semantic Web: • D. Fensel, J. Hendler, H. Lieberman and W. Wahlster, eds. Spinning the Semantic Web. Cambridge, MA: MIT Press, 2003. • J. Davies, D. Fensel and F. van Harmelen, eds. Towards the Semantic Web: Ontology-Driven Knowledge Management. New York: Wiley, 2002. • The conference series of the International Semantic Web Conference (see <http://www.semanticweb.org/>). TLFeBOOK TLFeBOOK
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TLFeBooK 2 Structured Web documents in XML 2.1 Introduction Today HTML(hypertext markup language) is the standard language in which Web pages are written. HTML, in turn, was derived from SGML (stan- dard generalized markup language), an international standard (Iso 8879)for the definition of device-and system-independent methods of representing information, both human- and machine-readable. Such standards are impor tant because they enable effective communication, thus supporting techno- logical progress and business collaboration. In the www area, standards are set by the W3C(World Wide Web Consortium); they are called recom- mendations, in acknowledgment of the fact that in a distributed environment without central authority, standards cannot be enforced Languages conforming to SGML are called SGML applications. HTML is such an application; it was developed because SGMl was considered far too complex for Internet-related purposes. XML (extensible markup language)is another SGML application, and its development was driven by shortcomings of HTML. We can work out some of the motivations for XML by considering Web page that information about a ch2>Nonmonotonic Reasoning: Context-Dependent Reasoning</h2> <i>by <b>v. Marek</b> and <b>M. Truszczynski</b></i><br> Springer 1993<br> ISBN0387976892 A typical XML representation of thethe same information might look like TLFeBOoK
2 Structured Web Documents in XML 2.1 Introduction Today HTML (hypertext markup language) is the standard language in which Web pages are written. HTML, in turn, was derived from SGML (standard generalized markup language), an international standard (ISO 8879) for the definition of device- and system-independent methods of representing information, both human- and machine-readable. Such standards are important because they enable effective communication, thus supporting technological progress and business collaboration. In the WWW area, standards are set by the W3C (World Wide Web Consortium); they are called recommendations, in acknowledgment of the fact that in a distributed environment without central authority, standards cannot be enforced. Languages conforming to SGML are called SGML applications. HTML is such an application; it was developed because SGML was considered far too complex for Internet-related purposes. XML (extensible markup language) is another SGML application, and its development was driven by shortcomings of HTML. We can work out some of the motivations for XML by considering a simple example, a Web page that contains information about a particular book. <h2>Nonmonotonic Reasoning: Context-Dependent Reasoning</h2> <i>by <b>V. Marek</b> and <b>M. Truszczynski</b></i><br> Springer 1993<br> ISBN 0387976892 A typical XML representation of the the same information might look like this: TLFeBOOK TLFeBOOK