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Introduction to RDF
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Introduction to RDF



A basic description about RDF, RDFs and why it is important to semantic web.

A basic description about RDF, RDFs and why it is important to semantic web.



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    Introduction to RDF Introduction to RDF Presentation Transcript

      • What is Semantic Web?
      • How it enables Semantic Web?
      • RDF
      • Triples - RDF Graph
      • Serialization Formats
      • RDFS
      • Resources
      • Q&A
    • What is Semantic Web?
      • Current Web: web of documents (html pages)
      • Semantic Web: web of data/things/concepts
        • What is a Thing/Concept? It can be any thing in the world - a movie, a person, a disease, a location…
        • Machines will be able to understand the concept behind a html page.
          • This page is talking about ‘ Barack Obama ’, He is a ‘ Person ’ and he is the ‘ President of USA ’ ?
    • How can we build Semantic Web?
      • A Straight forward way is to annotate all the data on the web.
      • Note: The semantics we are talking here is different from the semantics in NLP or NER perspective .
      • How do we annotate (explicitly add metadata) web?
        • Tags (simple but ambiguous, non-extensible)
        • Microformats (limited to a set of pre-defined vocabularies)
        • RDF (extensible, decentralized etc.)
    • RDF
      • RDF – Resource Description Framework
      • What is RDF?
        • A language to describe Resources.
      • What is a Resource?
        • Any thing/concept in the world: a book, a movie, a person etc.
        • must be identified by a universally unique name (URI)
      • What can we do with it?
        • Unambiguously describe a concept/resource/thing
        • Specify how these resources are related
        • Do basic inferencing
    • Where does it fit in Semantic Web Stack?
    • RDF – in detail
      • Knowledge is represented in RDF as a set of Triples .
      • What is a Triple?
        • Triple in RDF is analogous a sentence in natural language.
        • Every NL sentence contains 3 parts: subject, predicate & object. Similar is of the form <subject, predicate, object> and the purpose in RDF .
        • Example:
        • NL Sentence: Obama is the president of USA
        • RDF Triple: <URI1# Obama > <URI2# presidentOf > <URI3# USA >
        • Here subject & predicate must be resources (i.e they are things/concepts and must have a URI) and the object can be a resource or a literal (simple value. Eg: ‘10’)
      subject predicate object
    • RDF as a Graph
      • An RDF document is best visualized as a graph
      • Graph notations:
        • Resources (URI)
        • Literals (simple values)
        • Properties
      • Set of triples represented as a graph
      URI1#Obama URI2#USA 45 URI3#presidentOf URI3#age URI4#Person rdf:type
    • RDF – Serialization Formats
      • An RDF graph is a logical model, we need to serialize in some format.
      • What serialization Formats does RDF support?
        • RDF/XML (XML based syntax, popular)
        • NTriple (each triple is represented in one line)
        • Turtle etc.
        • N3
      • Example:
        • RDF/XML format:
          • <rdf:Description rdf:about=“URI1#Obama&quot;>
          • <rdf:type rdf:resource=“URI4#Person&quot; />
          • <URI2#isPresidentOf rdf:resource=“URI3#USA&quot; />
          • </rdf:Description>
        • NTriple format:
          • <URI1#Obama> <URI2#presidentOf> <URI3#USA>
          • <URI1#Obama> < http://www.w3.org/1999/02/22-rdf-syntax-ns#type> < URI4#Person>
    • RDFS
      • RDFS: RDF Schema
      • RDF Schema defines the basic vocabulary that can be used in RDF document to describe resources.
      • What exactly can we define:
        • Classes
        • Properties
        • Hierarchies
        • Collections
        • Reification
        • Documentation
        • Basic Entailments( subclass, subproperty) needed for reasoning
      • RDF Class is defined as:
      • <rdfs:Class rdf:ID=“someURI#Book”>
      • <rdfs:subClassOf rdf:resource=“someURI#FictionBook”/>
      • </rdfs:Class>
      RDFS Class Book FictionBook rdfs:subClassOf
      • Every property in RDF has :
      • Domain - Resource, which this property is part of
      • Range - Resource/Literal that is value of this property
        • <rdfs:Property rdf:ID=“ URI1#isPresidentOf ”>
      • <rdfs:domain rdf:resource=“ URI4#Person ”/>
      • <rdfs:range rdf:resource=“ URI5#Location ”/>
      • </rdfs:Property>
      RDFS Property URI1#isPresidentOf URI4#Person rdfs:domain rdfs:range URI5#Location
      • Class Entailments:
        • <Animals rdfs:subClassof LivingBeings>
        • <Cats rdfs:subClassOf Animals>
        • =>
        • <Cats rdfs:subClassOf LivingBeings>
      • Property Entailments:
        • <ParentOf rdfs: subPropertyOf AncestorOf>
        • <Fatherof rdfs: subPropertyOf ParentOf>
        • =>
        • <FatherOf rdfs: subPropertyOf AncestorOf>
      RDFS Entailments
      • Reification:
        • To make statements about statements
        • Eg: John said “Obama is the president of USA”
      • containers:
        • Bags - collection of resources, unordered
        • Sequences - collection of resources, ordered
        • Alt - only one resource of out of collection
      • rdf:seeAlso
        • Used to point extra information about the subject of this property
      Reification & others…
      • RSS 1.0 (RDF Site Summary)
      • RDFa (to add rdf metadata to html/xhtml pages – annotate the Web)
      • OWL (Successor of RDFS)
      Where is RDF currently used?
      • Importance of RDF in semantic web
      • RDF – syntax, graph model, serializations, examples
      • RDFS
      • Specs:
        • RDFS W3C Spec: http://www.w3.org/TR/rdf-schema/
        • RDF W3C Spec: http://www.w3.org/TR/REC-rdf-syntax/
      • Tutorials:
        • Semantic web: http://www.w3.org/2001/sw/
        • RDF Intro: http://www.rdfabout.com/intro/?section=contents
        • RDF in Detail: http://research.talis.com/2005/rdf-intro/
      • Not enough? Then check this: http://planetrdf.com/guide/
      • Q&A