Chapter 3 semantic web
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RDF handles limitations of XML by providing machine understandable documents that describe relationships between entities. The basic RDF model has three components - resources, properties, and statements. RDF can be represented using XML syntax or other syntactic representations. The RDF model represents relationships using a directed graph of these three components. Query languages like RQL and SPARQL can be used to query and retrieve information from RDF graphs.
Chapter 3 semantic web
- 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 2 Semantic Web.
- 3. Introduction • RDF has been given a syntax in XML – This syntax inherits the benefits of XML – Other syntactic representations of RDF possible Akerkar: Foundations of © Narosa Publishing House, 2009 3 Semantic Web.
- 4. RDF Model RDF Model Fundamental Model: Container Model: Resources, Bag, Sequence, Properties, Alternative Statements Akerkar: Foundations of © Narosa Publishing House, 2009 4 Semantic 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 5 Semantic 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 6 Semantic 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.html Akerkar: Foundations of © Narosa Publishing House, 2009 7 Semantic 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.jpeg Akerkar: Foundations of © Narosa Publishing House, 2009 8 Semantic 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 9 Semantic 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 10 Semantic 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 11 Semantic 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 12 Semantic 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 13 Semantic 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 Website Akerkar: Foundations of © Narosa Publishing House, 2009 14 Semantic 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 com Akerkar: Foundations of © Narosa Publishing House, 2009 15 Semantic 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 16 Semantic 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 17 Semantic 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 Gopal Akerkar: Foundations of © Narosa Publishing House, 2009 18 Semantic 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 19 Semantic 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 20 Semantic 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 21 Semantic Web.
- 22. Query Languages – RQL – SeRQL – Triple – RDQL – Rule ML Akerkar: Foundations of © Narosa Publishing House, 2009 22 Semantic Web.
- 23. Interoperability Akerkar: Foundations of © Narosa Publishing House, 2009 23 Semantic 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 24 Semantic 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 25 Semantic Web.