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Introduction to RDF

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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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Transcript

  • 1.
    • What is Semantic Web?
    • How it enables Semantic Web?
    • RDF
    • Triples - RDF Graph
    • Serialization Formats
    • RDFS
    • Resources
    • Q&A
    Agenda
  • 2. 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 ’ ?
  • 3. 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.)
  • 4. 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
  • 5. Where does it fit in Semantic Web Stack?
  • 6. 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
  • 7. 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
  • 8. 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>
  • 9. 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
  • 10.
    • 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
  • 11.
    • 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
  • 12.
    • 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
  • 13.
    • 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…
  • 14.
    • 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?
  • 15.
    • Importance of RDF in semantic web
    • RDF – syntax, graph model, serializations, examples
    • RDFS
    Recap
  • 16.
    • 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/
    Resources
  • 17.
    • Q&A