RD F and D A M L Resource D escription Fram ew ork (RD F)is a know ledge representation language represented in X M L. Itisa W WW Consortium Recom m endation. The D A RPA A gentM arkup Language (DAM L)isan extension ofRD F to serve as the basisforontology-based com puting overthe W eb:the Sem antic W eb .
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Motivation Dynamically identify and understand information sources Provide interoperability between agents in a semantic manner Enable distributed extensible.
DAML+OIL RDF DAML+OIL ontology is a set of RDF statements –http://www.daml.org/2001/03/daml+oil.daml Ontology can actually include arbitrary RDF statements RDF schema uses XML syntax, but could theoretically use any other syntax
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RDF and DAML
Resource Description Framework (RDF) is a knowledge representation language represented in XML. It is a WWW Consortium Recommendation.
The DARPA Agent Markup Language (DAML) is an extension of RDF to serve as the basis for ontology-based computing over the Web: the Semantic Web.
Motivation• Dynamically identify and understand
information sources • Provide interoperability between agents
in a semantic manner • Enable distributed extensible network of
ontologies • Current tools such as HTML, XML not
sufficient to express semantics, relationships between classes
DAML+OIL <-> RDF
• DAML+OIL ontology is a set of RDF statements – http://www.daml.org/2001/03/daml+oil.daml
• Ontology can actually include arbitrary RDF statements
• RDF schema uses XML syntax, but could theoretically use any other syntax
XML• Makes use of tags just like HTML, but arbitrary
in subject verb object (SVO) form Within the obligatory RDF declaration (typically a tag that begins something like <rdf:RDF ...), each topmost element is the subject of a sentence. The next level of enclosed elements represent verb/object pairs for this sentence:<Class ID="Male"> <subClassOf resource="#Animal"/> </Class> Male is a subclass of Animal.
<Class ID="Female"> <subClassOf resource="#Animal"/> <disjointWith resource="#Male"/> </Class> Female is a subclass of Animal AND Female is disjoint from Male. The single subject -- Female -- is used to begin each of the verb-object assertions<subClassOf resource="#Animal"/> and<disjointWith resource="#Male"/>
Basic RDF object types
• Resources – All things being described by RDF expressions – Identified by URI plus optional anchor id– E.g., <disjointWith resource="#Male"/>
• Properties – A specific aspect, characteristic, attribute, or
relation used to describe a resource – has a specific meaning, defines its permitted
values, the types of resources it can describe, and its relationship with other properties
Basic RDF object types cont.
• Statements – A specific resource together with a named
property plus the value of that property for that resource is an RDF statement
– Called the subject, the predicate, and the object
– property value can be another resource or it can be a literal(string or other primitive data type)
Simple Example cont.1• Now, consider the case that we want to say something
more about the characteristics of the creator of this resource. In prose, such a sentence would be:The individual whose name is Ora Lassila, email <[email protected]>, is the creator of http://www.w3.org/Home/Lassila.
The intention of this sentence is to make the value of the Creator property a structured entity. In RDF such an entity is represented as another resource. The sentence above does not give a name to that resource; it is anonymous, so in the diagram below we represent it with an empty oval:
Simple Example cont.2The structured entity of the previous example can also be
assigned a unique identifier. To continue the example, imagine that an employee id is used as the unique identifier for a "person" resource. The URIs that serve as the unique keys for each employee (as defined by the organization) might then be something like http://www.w3.org/staffId/85740. Now we can write the two sentences:The individual referred to by employee id 85740 is named Ora Lassila and has the email address [email protected]. The resource http://www.w3.org/Home/Lassila was created by this individual.
Abbreviated Syntax Form 1
• Usable for properties that are not repeated within a description and where the values of those properties are literals
• the properties may be written as XML attributes <rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila" s:Creator="Ora Lassila" /> </rdf:RDF>
• Side effect: might be viewed differently in browser
Abbreviated Syntax Form 2
• Works for nested Description elements <rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator rdf:resource="http://www.w3.org/staffId/85740"/>
propName resourceAttr '/>' [7] propName ::= Qname [8] value ::= description | string [9] resourceAttr ::= 'resource="' URI-reference '"' [10] Qname ::= [ NSprefix ':' ] name [11] URI-reference ::= string, interpreted per [URI] [12] IDsymbol ::= (any legal XML name symbol) [13] name ::= (any legal XML name symbol) [14] NSprefix ::= (any legal XML namespace prefix) [15] string ::= (any XML text, with "<", ">", and "&" escaped)
RDF/XML
Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila. is represented in RDF/XML as:<rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator>Ora Lassila</s:Creator> </rdf:Description> </rdf:RDF>