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Semantic Web

Semantic Web. Thanks to folks at LAIT lab Sources include : Tim Berners-Lee Presentation W3C Semantic Web Activity Presentation of W3C and Semantic Web by Eric Prudhommeaus. What is XML. HTML describes document structure and presentation

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Semantic Web

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  1. Semantic Web Thanks to folks at LAIT lab Sources include : • Tim Berners-Lee Presentation • W3C Semantic Web Activity • Presentation of W3C and Semantic Web by Eric Prudhommeaus

  2. What is XML • HTML describes document structure and presentation • XML is meta-language used to define other domain or industry specific language • XML addresses “structuring” of data rather than documents • XML documents by themselves, bear no semantics Separation of Content from Presentation

  3. XML and Semantics • XML Documents do not have semantics • One uses XML to define an XML language adhering to a particular DTD • XML documents can have semantics only by convention • Implicit Semantic agreement on paper within a community of users for a particular domain data

  4. Semantic Web • 1st generation, Internet enabled disparate machines to exchange data • 2nd generation, enabled new applications on top of growing internet, making enormous amounts of information available, in human-readable form, and allowing revolution in new applications B2C • The next generation of the net is an “agent-enabled” (Semantic Web) which makes information available in machine-readable form …. enabling “agent” communication at a Web-wide scale

  5. Semantic Web • The Semantic Web is a vision: the idea of having data on the web defined and linked in a way that it can be used by machines • The Semantic Web approach proposes languages for expressing information and the relationships between information. … Over time, these languages will accommodate additional formal systems techniques for verification of logical consistency and for reasoning” - W3C Semantic Web Activity Statement

  6. Tim Berners- Lee’s Vision of Semantic Web

  7. RDF & RDFS • Provide a data model and syntax convention for representing the semantics of data in standardized interoperable manner • Describe relationships among resources as “subject-verb-object” triples and properties & values • RDFS – Minimal ontology modeling language, object oriented type system Semantics remain Under-Specified

  8. RDF Example <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:s="http://www.w3.org/2001/02/acls/ns#">   <rdf:Bag ID="B1">      <rdf:li>      <s:resourceAccessRule rdf:ID="U2" s:access="get,put,delete">                 <s:accessor rdf:resource="http://umbc.edu/group=w3cteamgroup"/>              </s:resourceAccessRule></rdf:li>   </rdf:Bag>   <rdf:Description aboutEach="#B1">      <s:hasAccessTo rdf:resource="http://www.w3.org/2001/Talks/0710-ep-grid/all.htm"/>   </rdf:Description> </rdf:RDF>

  9. RDFS Example <rdfs:Class ID="ResourceAccessRule">  <rdfs:label xml:lang="en">Access Rule</rdfs:label>  <rdfs:comment>An assertion of access privileges to a resource.</rdfs:comment>  <rdfs:isDefinedBy resource="http://www.w3.org/2001/02/acls/ns#"/></rdfs:Class> <rdf:Property ID="hasAccessTo">  <rdfs:label xml:lang="en">has access to</rdfs:label>  <rdfs:comment>Relates an Access Rule to the resources to which the rule applies.  The inverse relation is 'accessedBy'</rdfs:comment>  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>  <rdfs:domain rdf:resource="#ResourceAccessRule"/>  <rdfs:isDefinedBy resource="http://www.w3.org/2001/02/acls/ns#"/></rdf:Property>

  10. Ontology Layer • A common vocabulary an agreed upon meanings to describe a subject domain • Widens interoperability & inter-conversion • More meta-information such as • Transitive property • Unique, unambiguous, cardinality etc. More Semantically Rich

  11. DAML + OIL • Goal to define language(s) for the Semantic Web • Build on top of RDF and XML • Adds more constraints to RDF • Allows definition, sharing, composition and use of ontologies • Frame based knowledge representation language • Add meta-data about anything which has URI

  12. DAML+OIL Example • <rdf:Property ID="memberOf">  <rdf:type  • rdf:resource="http://www.ontoknowledge.org/oil/rdf-schema/2000/11/10-oil standard#TransitiveProperty"/>  <rdfs:label xml:lang="en">member of</rdfs:label>  <rdfs:comment>The relationship of a member of a group to that group.</rdfs:comment>  <rdfs:range rdf:resource="#Group"/>  <rdfs:domain rdf:resource="#Principle"/>  <rdfs:isDefinedBy resource="http://www.w3.org/2001/02/acls/ns#"/></rdf:Property>

  13. Semantic Web • Logic • I am an employee of UMBC.UMBC is a member of W3C.UMBC has GET access to http://www.w3.org/Member/.I (therefore) have access to http://www.w3.org/Member/. • Proof • UMBC's document employList lists me as an employee.W3C'c member list includes UMBC.The ACLs for http://www.w3.org/Member/ assert that employees of members have GET access. • Trust • UMBC's document employList is signed by a private key that W3C trusts to make such assertions.W3C'c member list is trusted by the access control mechansim.The ACLs for http://www.w3.org/Member/ were set by an agent trusted by the access control mechanism. • Making the simple stuff simple and the complex stuff possible.

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