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The Semantic Web – WEEK 4: RDF Tutorial/Practical: Exercises using the Suns Lee McCluskey NB most examples below courtesy of the RDF Primer WC3 document.

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Presentation on theme: "The Semantic Web – WEEK 4: RDF Tutorial/Practical: Exercises using the Suns Lee McCluskey NB most examples below courtesy of the RDF Primer WC3 document."— Presentation transcript:

1 The Semantic Web – WEEK 4: RDF Tutorial/Practical: Exercises using the Suns Lee McCluskey NB most examples below courtesy of the RDF Primer WC3 document

2 The Semantic Web Recap n Last week we saw how complex data structures can be SPECIFIED in XML Schema documents. n These are then used as the validating definitions of XML documents. The elements defined in the Schema give us a ‘namespace’. n XML Schema are considered better than DTD’s as they are XML docs, they are more expressive etc

3 The Semantic Web RDF - the Resource Description Framework The web is like an enormous library with no structure. The purpose of RDF is to act as a uniform or standard language for describing and representing information about Web resources or things identifiable on the Web. This will mean a change from the current ‘brute force’ search engines to much more powerful services…

4 The Semantic Web RDF vs XML Main difference between XML and RDF (and higher level languages like OWL) n RDF/ RDFS have a FIXED and pre-defined set of tags -XML does not. n For scalability, we need a fairly standard format for documents (eg RDF’s list of triples). n RDF application area more specific than XML – describing properties of ‘web resources’

5 The Semantic Web RDF - basis n everything having a URI = Universal Resource Identifier n Properties - resources with a ‘name’ such as slots in an object frame n An RDF document is a series of Statements which are triples - (Resource, Property, Value) Or (Subject, Predicate, Object) NB the Property/Predicate is NOT functional – there can be many values for the same resource+property

6 The Semantic Web RDF example RDF ~ set of (Resource, Property, Value) "The Author of is Lee McCluskey.” IN RDF: Lee McCluskey Resource, Property, Values can all have URI’s

7 The Semantic Web RDF example Lee McCluskey Author The orange box denotes a literal - literals may not be used as subjects or predicates in RDF statements, only objects.

8 The Semantic Web RDF - QNames n RDF (and XML) docs rely on short hand to keep their size down. One mechanism is called the Qualified Name or QName. Example: Start of document we might have.. fred = Then where ever we see ‘fred:subject’ we read

9 The Semantic Web RDF - QNames Common QNames used throughout the semantic web: rdf: refers to namespace URI: rdfs: refers to namespace URI: owl: refers to namespace URI: xsd: refers to namespace URI: dc: refers to namespace URI: dc is the ‘Dublin Core’ – meta data convention for describing documents

10 The Semantic Web RDF example Example below shows.. n Multiple property/values shorthand n Value that is a URI is an attribute [example 1] August 16, 1999 en Here ‘exterms’ is some pre-defined vocabulary..

11 The Semantic Web Examples - rdf:type’s.. are properties that describe the resources as instances of specific types or classes [example 2] Overnighter OR…………………… [example 3] Overnighter

12 The Semantic Web Eric Miller Dr. from W3C RDF Primer [example4]

13 The Semantic Web Blank Nodes RDF allows only Binary Predicates This can cause problems where an object has a property that has many facets eg Person’s address Person’s DoB …../:fred_bloggs june1931 Date:year Date:month

14 The Semantic Web [example 5] RDF/XML Syntax Specification (Revised) Dave Beckett Example from “W3C RDF Primer”

15 The Semantic Web RDFS - RDF Schema = RDF + classes, properties of properties, etc - gives more structure to RDF RDF is expanded by new tags such as rdf:Class rdf:Property rdf:label which allow vocabulary – schema to be written (in a similar manner to xml schema)

16 The Semantic Web Vocabularies…. n RDF/RDFS allows anyone to write their own name-space document (a ‘schema’). This defines properties and classes in some application domain n These form vocabularies which can be used globally for sharing the meaning of tags

17 The Semantic Web..and Ontologies Vocabularies are like Ontologies….! An Ontology is a formalised conceptual structure

18 The Semantic Web Summary n RDF is a standard language for describing meta-data for the web. n It is an XML application. n It consists, basically, of sets of triples (statements) of the form “subject, predicate, object” n RDF Schema is a way of introducing classes/instances of resources


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