Introduction to RDF
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The document discusses the Semantic Web and Resource Description Framework (RDF). It defines the Semantic Web as making web data machine-understandable by describing web resources with metadata. RDF uses triples to describe resources, properties, and relationships. RDF data can be visualized as a graph and serialized in formats like RDF/XML. RDF Schema (RDFS) provides a basic vocabulary for defining classes, properties, and hierarchies to enable reasoning about RDF data.
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Introduction to RDF
- 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"> <rdf:type rdf:resource=“URI4#Person" /> <URI2#isPresidentOf rdf:resource=“URI3#USA" /> </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#FictionBook”> <rdfs:subClassOf rdf:resource=“someURI#Book”/> </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