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

Separation of Content from Presentation 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

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

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

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

Tim Berners- Lee’s Vision of Semantic Web

Semantics remain Under-Specified 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

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>

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>

More Semantically Rich 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

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

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>

Semantic Web Logic Proof Trust 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.