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Chapter 1 The Semantic Web
Introduction• World Wide Web: wide-area hypermedia information retrieval initiative aiming to give universal access to a large universe of documents.• The challenge of the Semantic Web, according to Berners-Lee: – To provide a language that expresses both data and rules for reasoning about the data and that allows rules from any existing knowledge representation system to be exported onto the Web.Akerkar: Foundations of © Narosa Publishing House, 2009 2Semantic Web.
Introduction• Example 1.1: let us assume that Gopal is a professor. – The Web wakes him up based on his lecture schedule as well as depending on the day of the week. – Web informs him about his schedule and appointments. He could also get the details of how to reach a particular destination on that day. – He could further informed of locations of his personal accessories. – The Web manages all sorts of dynamic situations such as unexpected events. – On weekends, when he completes his work for the day, the Web makes arrangements for him to meet his wife and kids for dinner in a restaurant in the city.• Web has completely taken over Gopal’s life and it makes life easier but it is also up to Gopal to follow the advice given by the Web.Akerkar: Foundations of © Narosa Publishing House, 2009 3Semantic Web.
Evolution of the Web Web in 1995 Web in 2000 Web in 2008 HTML, XML HTML, XML, RDF HTMLAkerkar: Foundations of © Narosa Publishing House, 2009 4Semantic Web.
Hyper Text Transfer Protocol• The request line from the client consists of a request method, the address of the file requested and the HTTP version number. GET /mypage.html HTTP/1.1 – The above request calls for mypage.html file using the GET HTTP method;• A header looks like: ACCEPT: */* ACCEPT_LANGUAGE:en-us REFERER:http://www.ntnu.org/dev03.html USER_AGENT:FireFox/5.0 (compatible; MSIE 6.01; Windows NT 6.0)Akerkar: Foundations of © Narosa Publishing House, 2009 5Semantic Web.
Uniform Resource Identifier• URL stands for Uniform Resource Locator, which means it is a uniform (same throughout the world) way to locate a resource (file or document) on the Internet.• A Uniform Resource Identifier (URI) is an identifier used to identify objects in a space. URL is written as http://www.tmrfindia.org Various URI schemes are, • ftp://ftp.ac.bolt.org/class/class237.txt • http://www.bolt.org/class/class123.txt • ldap://[2003:db7::3]/c=GB?objectClass?one • mailto:firstname.lastname@example.org • news:comp.infosystems.www.servers.unix • tel:+91-230-247-7876 • telnet://184.108.40.206:80/Akerkar: Foundations of © Narosa Publishing House, 2009 6Semantic Web.
A Layered Cake (W3C)A layered cake consists of: – Extensible Markup Language (XML): – XML Schema: – Resource Description Framework (RDF): – RDF Schema: – Ontology: – Logic and Proof: – Trust:Akerkar: Foundations of © Narosa Publishing House, 2009 7Semantic Web.
Semantic Web Technologies The Semantic Web InformationXML, RDF, Metadata, Database Technology: Management Agent Technology: Ontologies, Data Transactions, Metadata, Technology: DAMLModelling Technologies Storage, Query Collaboration, Knowledge ManagementAkerkar: Foundations of © Narosa Publishing House, 2009 8Semantic Web.
Ontology• Definition 1.1: An ontology is a formal, explicit specification of a shared conceptualization. – Ontologies describe data models in terms of classes, subclasses, and properties. – For instance, we can define a man to be a subclass of human, which in turn is a subclass of animals that is a biped i.e. walks on two legs. – Ontologies are mainly categorized into two types: – general ontologies (like SENSUS, Cyc, WordNet, etc.) – domain-specific ontologies (like, GALEN – Generalized Architecture for Languages, Encyclopedias, and Nomenclatures in medicine; UMLS - Unified Medical Language System).Akerkar: Foundations of © Narosa Publishing House, 2009 9Semantic Web.
Semantics• Definition 1.2: Semantic is a study of meaning and changes of meaning.• The different types of semantics are: – Denotational Semantics: – Operational Semantics: – Axiomatic semantics: – Model-Theoretic Semantics:Akerkar: Foundations of © Narosa Publishing House, 2009 10Semantic Web.
Web Service – Web Services is • self-contained, • self-describing, • modular applications that can be published, located, and invoked across the Web.Akerkar: Foundations of © Narosa Publishing House, 2009 11Semantic Web.
Semantic Web Mining• The Semantic Web – to organize and browse the Web in ways more suitable to the problems they have at hand. – to impose a conceptual filter to a set of Web pages, and display their relationships based on such a filter. – to visualization of complex content. With HTML, such interfaces are virtually impossible since it is difficult to extract meaning from the text.• The major concern of Semantic Web is to convert the World Wide Web from just a huge repository of unrelated text, into useful linked pieces of information. – Linking the information is not only based on text similarity, but mainly on the meanings and real-world relations between items.Akerkar: Foundations of © Narosa Publishing House, 2009 12Semantic Web.
Book Overview• Chapter 2: XML is a universal language for defining markup, it does not provide with any means of talking about the semantics (i.e. meaning) of data. XML helps Web document to become structured document. This structure of a document can be made machine-accessible through DTDs and XML schema.• Chapter 3: RDF is a language for describing resources and RDF Schema is a primitive ontology language. Both, RDF and RDF Schema, provide the core languages for the Semantic Web.• Chapter 4: This chapter deals with concept of ontology and ontology languages. Here, we will also present some of the practical issues that arise when building ontologies.• Chapter 5: We will present some useful concepts from knowledge representation and reasoning, especially description logic. This is a backbone of some ontology languages.• Chapter 6: This chapter presents some issues for building Semantic Web. Actually, it is very difficult to predict the architecture of Semantic Web.• Chapter 7: The chapter discusses a wide-ranging outline of the kinds of techniques to which Semantic Web technology can be applied.Akerkar: Foundations of © Narosa Publishing House, 2009 13Semantic Web.
Suggested Reading – T. Berners-Lee, J. Hendler and O. Lassila. The Semantic Web. Scientific American 284, 5, May 2001: 34-43. – T. Berners-Lee. Weaving the Web. Harper 1999. – T. Berners-Lee. Semantic Web Road Map. http://www.w3.org/DesignIssues/Semantic – T. Berners-Lee. Evolvability. http://www.w3.org/DesignIssues/Evolution.html – T. Berners-Lee. What the Semantic Web can represent. http://www.w3.org/DesignIssues/RDFnot.htmlAkerkar: Foundations of © Narosa Publishing House, 2009 14Semantic Web.