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Chapter 3 semantic web
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  • 1. Chapter 3 Resource Description Framework
  • 2. Introduction• RDF handles limitations of XML in providing machine understandable documents. – Feature of RDF is that it provides better support for interoperability and describes not only contents of document but also relationships between various entities within the document.• Basic model of RDF has three types: – resources, – properties, and – Statements (Values).Akerkar: Foundations of © Narosa Publishing House, 2009 2Semantic Web.
  • 3. Introduction• RDF has been given a syntax in XML – This syntax inherits the benefits of XML – Other syntactic representations of RDF possibleAkerkar: Foundations of © Narosa Publishing House, 2009 3Semantic Web.
  • 4. RDF Model RDF Model Fundamental Model: Container Model: Resources, Bag, Sequence, Properties, Alternative StatementsAkerkar: Foundations of © Narosa Publishing House, 2009 4Semantic Web.
  • 5. Introduction• Example 3.1: Typical parts of URIs are, http://www.tmrfindia.in:8080/secret/top.jsp?id=12&from=2 |Scheme|----------Host--------------|-Port--|---------Path-----------|-----Query-------| |---------------------------------Scheme-specific part---------------------------|Akerkar: Foundations of © Narosa Publishing House, 2009 5Semantic Web.
  • 6. Introduction• Definition 3.1 : Resource Description Framework (RDF) is a framework that can be used in many different contexts to achieve different goals.• RDF model is a combination of three parts, namely: – Resource: Any entity that has to be described is known as Resource or Object. It can be a ‘Web page’ on Internet or an ‘individual’ in a community. – Property: Any characteristic of Resource or its attribute, which is used for the description of the same, is known as Property or Predicate. For example, a Web page may be known by ‘Title’ or an individual is recognized by his ‘Name’. Thus, both are attributes for recognition of Resource ‘Web page’ and ‘individual’, respectively. – Value: A Property must have a value. For instance, the title of an Organization Web page is ‘TQ Pioneer Ltd.’, or name of an individual is ‘Gopal’.Akerkar: Foundations of © Narosa Publishing House, 2009 6Semantic Web.
  • 7. Example 3.2• The triple in Figure 3.2 can be interpreted as Gopal is the creator of the resource http://www.tmrfindia.org/main.html. – Here subject (resource) is http://www.tmrfindia.org/main.html and predicate (property) is http://purl.org/dc/Creator http:// mailto:gopal@tmrf www.tmrfindia.org/ http://purl.org/DC/Creator india.org main.htmlAkerkar: Foundations of © Narosa Publishing House, 2009 7Semantic Web.
  • 8. Example 3.3• The RDF directed graph that a resource may have more than one value for a given property. http:// mailto:gopal@ www.tmrfindia. http://purl.org/dc/Creator tmrfindia.org org/main.html http://www.example.in/ http://www.example.in/ schema/include schema/colleague http://purl.org/dc/Creator http:// mailto:gita@ www.tmrfindia. tmrfindia.org org/logo.jpegAkerkar: Foundations of © Narosa Publishing House, 2009 8Semantic Web.
  • 9. Vocabulary• A vocabulary is a list of predefined values.• rdf:Resource – It is an attribute of a property element.• rdf:Property – The properties are special type of resources used as predicate of triples; the semantics of a triple clearly depends on the property used as predicate.Akerkar: Foundations of © Narosa Publishing House, 2009 9Semantic Web.
  • 10. Vocabulary• rdf:Statement – A statement is a resource reifying a triple. It emphasizes the properties of resources• rdfs:subPropertyOf – Any property denotes a relation between resources. rdfs:subPropertyOf applies to properties• rdfs:Class, rdf:type and rdfs:subClassOf – Classes are resources denoting a set of resources, by the mean of the property rdf:type (instances have property rdf:type valued by the class). All properties have rdf:type valued by rdf:Property.Akerkar: Foundations of © Narosa Publishing House, 2009 10Semantic Web.
  • 11. Vocabulary• rdfs:domain and rdfs:range – rdfs:domain is a property used to indicate that a particular property applies to a designated class (i.e. domain of the property). – rdfs:range is a property used to indicate that the values of a particular property are instances of designated class.Akerkar: Foundations of © Narosa Publishing House, 2009 11Semantic Web.
  • 12. Vocabulary• rdfs:Literal – rdfs:Literal, denoting the set of literals, is declared as a class. Its intended use is to be the range of properties.• rdfs:Container – Containers are collections of resources.Akerkar: Foundations of © Narosa Publishing House, 2009 12Semantic Web.
  • 13. Example 3.8• Here we present a simple XML syntax. <?xml version="1.0" encoding="UTF-8" ?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/" xmlns:os="http://www.example.in/schema/"> <rdf:Description about="http://www.tmrfindia.org/main.html"> <dc:Creator rdf:resource="mailto:gita@tmrfindia.org"/> <dc:Title> Main Website </dc:Title> <dc:Creator> <rdf:Description about="mailto:gopal@tmrfindia.org"> <os:colleague rdf:resource="mailto:gita@tmrfindia.org"/> </rdf:Description> </dc:Creator> </rdf:Description> </rdf:RDF>Akerkar: Foundations of © Narosa Publishing House, 2009 13Semantic Web.
  • 14. XML Syntax http:// mailto:gopal@tmrf www.tmrfindia.org http://purl.org/dc/Creator india.org /main.html http://www.example.in/ schema/colleague http://purl.org/dc/Creator http://www.purl.org/dc/Main mailto:gita@tmrf india.org Main WebsiteAkerkar: Foundations of © Narosa Publishing House, 2009 14Semantic Web.
  • 15. Example 3.10• Illustrate a diagram to representing the following statements in RDF data model: The creator of the resource http://www.hotmail.com is Sabeer Bhatia. <?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:s="http://description.org/schema/"> <rdf:Description rdf:about="http://www.hotmail.com"> <s:Creator>Sbeer Bhatia</s:Creator> </rdf:Description> </rdf:RDF> http:// http://www.description.org/ Sabeer www.hotmail. schema/Creator Bhatia comAkerkar: Foundations of © Narosa Publishing House, 2009 15Semantic Web.
  • 16. Example 3.11<?xml version="1.0" encoding="UTF-8" ?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22- http:// http:// rdf-syntax-ns#"> www.tmrfindia.org rdf_1 www.tmrfindia.org/ /main.html main.html <rdf:Bag ID="mybag"> <rdf:li resource="http://www.tmrfindia.org /main.html"/> rdf_3 <rdf:li rdf_2 resource="mailto:gopal@tmrfindia.org"/> <rdf:li> XYZ </rdf:li> mailto:gopal@tmrf india.org "XYZ" </rdf:Bag></rdf:RDF>Akerkar: Foundations of © Narosa Publishing House, 2009 16Semantic Web.
  • 17. Example 3.12• The description is, <rdf:Description rdf:ID=”ding”> <library:name>R. Akerkar</library.name> </rdf:description>• This can be refined as below, where rdf:subject, rdf:predicate, rdf:object allow us to access the parts of a statement. <rdf:Statement rdf:ID=”StatementIDding”> <rdf:subject rdf:resource=”ding”/> <rdf:predicate rdf:resorce=”&library;name”/> <rdf:object>R. Akerkar</rdf:object> </rdf:Statement>Akerkar: Foundations of © Narosa Publishing House, 2009 17Semantic Web.
  • 18. Example 3.13 s:Creator http://www.tmrfindia.org/main.html rdf:subject rdf:predicate s:Creator rdf:type rdf:object rdf:Statement b:believed Amit GopalAkerkar: Foundations of © Narosa Publishing House, 2009 18Semantic Web.
  • 19. RDF Schema• Example 3.16: In the following schema, the resource "car" is a subclass of the class "vehicle". <?xml version="1.0"?> <rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.vehicle.org/vehicles#"> <rdf:Description rdf:ID="vehicle"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> </rdf:Description> <rdf:Description rdf:ID="car"> <rdf:type rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/> <rdfs:subClassOf rdf:resource="#vehicle"/> </rdf:Description> </rdf:RDF>Akerkar: Foundations of © Narosa Publishing House, 2009 19Semantic Web.
  • 20. RDF Schema• Previous example is modified with the help of rdfs:Class instead of rdf:Description, and drop the rdf:type information. <?xml version="1.0"?> <rdf:RDF xmlns:rdf= "http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xml:base= "http://www.vehicle.org/vehicles#"> <rdfs:Class rdf:ID="vehicle" /> <rdfs:Class rdf:ID="car"> <rdfs:subClassOf rdf:resource="#vehicle"/> </rdfs:Class> </rdf:RDF>Akerkar: Foundations of © Narosa Publishing House, 2009 20Semantic Web.
  • 21. Query Languages• Basic approaches to query RDF metadata: – SQL style approach that considers RDF metadata as a relational or XML database and derives API methods to query the object classes. – Knowledge Representation style approach that considers the link structure illustrated by RDF metatdata as a Web knowledge base and further applies knowledge representation and reasoning technologies on it.Akerkar: Foundations of © Narosa Publishing House, 2009 21Semantic Web.
  • 22. Query Languages – RQL – SeRQL – Triple – RDQL – Rule MLAkerkar: Foundations of © Narosa Publishing House, 2009 22Semantic Web.
  • 23. InteroperabilityAkerkar: Foundations of © Narosa Publishing House, 2009 23Semantic Web.
  • 24. RDF Disadvantages – The RDF format restricts you on how you design your XML. – RDF uses namespaces to uniquely identify types (classes), properties, and resources. – In order to use the RDF format, you have to learn the extensive RDF vocabulary.Akerkar: Foundations of © Narosa Publishing House, 2009 24Semantic Web.
  • 25. Suggested Readings 1. R. Akerkar and P. Lingras. Building an Intelligent Web: Theory & Practice, Johns & Bartlett, 2007. 2. T. Berners-Lee, R. Fielding, U.C. Irvine, and L. Masinter. Uniform Resource Identifiers (URI): Generic Syntax. urn:ietf:rfc:2396, 1998. 3. D. Brickley and R.V. Guha. Resource Description Framework (RDF) Schema Specification, W3C proposed recommendation, 1999. 4. R. Fikes and D. L McGuinness. An Axiomatic Semantics for RDF, RDF Schema, and DAML-ONT. KS Lab, Stanford University, 2001. 5. O. Lassila and R. R. Swick. Resource Description Framework (RDF) Model and Syntax Specification, W3C recommendation, 1999.Akerkar: Foundations of © Narosa Publishing House, 2009 25Semantic Web.