1 / 31

Motivation

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.

ally
Download Presentation

Motivation

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. 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

  3. XML • Makes use of tags just like HTML, but arbitrary <aTag>...</aTag> <anEmptyTag/> <anotherTag with="an attribute">...</anotherTag> <aTag>with <anemptyTag/> inside it</aTag> <tags>and<moreTags>and<yetmoreTags>and...</yetmoreTags></moreTags></tags> • Tags can be defined semantically in a DTD

  4. RDF • RDF document is a collection of assertions 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.

  5. <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"/>

  6. 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

  7. 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) • http://www.w3.org/RDF/

  8. Simple Example • Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila <rdf:RDF xmlns:rdf=“http://www.w3.org/1999/02/22-rdf-syntax-ns#” xmlns:s="http://description.org/schema/"> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator>Ora Lassila</s:Creator> </rdf:Description> </rdf:RDF>

  9. 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 <lassila@w3.org>, 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:

  10. Simple Example cont.2 The 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 lassila@w3.org. The resource http://www.w3.org/Home/Lassila was created by this individual.

  11. 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

  12. 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"/> </rdf:Description> <rdf:Description about="http://www.w3.org/staffId/85740"> <v:Name>Ora Lassila</v:Name> <v:Email>lassila@w3.org</v:Email> </rdf:Description> </rdf:RDF> equal to <rdf:RDF> <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator rdf:resource="http://www.w3.org/staffId/85740" v:Name="Ora Lassila" v:Email="lassila@w3.org" /> </rdf:Description> </rdf:RDF>

  13. Abbreviated Syntax Form 3 • description element containing a type property <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator> <rdf:Description about="http://www.w3.org/staffId/85740"> <rdf:type resource="http://description.org/schema/Person"/> <v:Name>Ora Lassila</v:Name> <v:Email>lassila@w3.org</v:Email> </rdf:Description> </s:Creator> </rdf:Description> equal to <rdf:Description about="http://www.w3.org/Home/Lassila"> <s:Creator> <s:Person about="http://www.w3.org/staffId/85740"> <v:Name>Ora Lassila</v:Name> <v:Email>lassila@w3.org</v:Email> </s:Person> </s:Creator> </rdf:Description>

  14. Basic Serialization Syntax Basic RDF serialization syntax takes the form: [1] RDF ::= ['<rdf:RDF>'] description* ['</rdf:RDF>'] [2] description ::= '<rdf:Description' idAboutAttr? '>' propertyElt* '</rdf:Description>' [3] idAboutAttr ::= idAttr | aboutAttr [4] aboutAttr ::= 'about="' URI-reference '"' [5] idAttr ::= 'ID="' IDsymbol '"' [6] propertyElt ::= '<' propName '>' value '</' propName '>' | '<' 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)

  15. 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>

  16. RDF schema • Different from XML DTD: syntax vs. semantics • Defines Class, Property, subClassOf, subPropertyOf, domain, range, and some others • http://www.w3.org/TR/rdf-schema/http://www.w3.org/TR/REC-rdf-syntax/

  17. Why RDF Is Not Enough • Only range/domain constraints on properties (need others) • No properties of properties (unique, transitive, inverse, etc.) • No equivalence, disjointness, etc. • No necessary and sufficient conditions (for class membership) • No defined semantics

  18. DAML basics • Setting up the namespaces <rdf:RDF xmlns:rdf =http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:rdfs=http://www.w3.org/2000/01/rdf-schema# xmlns:daml=http://www.daml.org/2000/12/daml+oil# xmlns =“http://www.daml.org/2000/12/daml+oil-ex#”

  19. DAML basics cont.1 • Assert an ontology <daml:Ontology rdf:about=“”> <daml:versionInfo>$Id: daml+oil-ex.daml,v 1.4 2001/01/11 20:33:52 mdean Exp $</daml:versionInfo> <rdfs:comment> An example ontology </rdfs:comment> <daml:imports rdf:resource=“http://www.daml.org/2000/12/daml+oil/> </daml:Ontology>

  20. DAML basics cont.2 • Define classes <rdfs:Class rdf:ID="Animal"> <rdfs:label>Animal</rdfs:label> <rdfs:comment> This class of animals is illustrative of a number of ontological idioms. </rdfs:comment> </rdfs:Class> <rdfs:Class rdf:ID="Male"> <rdfs:subClassOf rdf:resource="#Animal"/> </rdfs:Class>

  21. DAML basics cont.3 • Define classes • <rdfs:Class rdf:ID="Female"> <rdfs:subClassOf rdf:resource="#Animal"/> <daml:disjointWith rdf:resource="#Male"/> </rdfs:Class> <rdfs:Class rdf:ID="Man"> <rdfs:subClassOf rdf:resource="#Person"/> <rdfs:subClassOf rdf:resource="#Male"/> </rdfs:Class>

  22. DAML basics cont.4 • Define properties • <rdf:Property rdf:ID="hasParent"> • <rdfs:domain rdf:resource="#Animal"/> <rdfs:range rdf:resource="#Animal"/> </rdf:Property> • <rdf:Property rdf:ID="hasFather"> <rdfs:subPropertyOf rdf:resource="#hasParent"/> <rdfs:range rdf:resource="#Male"/> </rdf:Property>

  23. DAML basics cont.5 • Define restrictions <rdfs:Class rdf:ID="Person"> <rdfs:subClassOf rdf:resource="#Animal"/> <rdfs:subClassOf> <daml:Restriction>scope difference <daml:onProperty rdf:resource="#hasParent"/> <daml:toClass rdf:resource="#Person"/> </daml:Restriction> </rdfs:subClassOf> <rdfs:subClassOf> <daml:Restriction daml:cardinality="1"> <daml:onProperty rdf:resource="#hasFather"/> </daml:Restriction> </rdfs:subClassOf> </rdfs:Class>

  24. DAML basics cont.6 About tag <rdfs:Class rdf:about="#Animal"> <rdfs:comment> Animals have exactly two parents, ie: If x is an animal, then it has exactly 2 parents (but it is NOT the case that anything that has 2 parents is an animal). </rdfs:comment> <rdfs:subClassOf> <daml:Restriction daml:cardinality="2"> <daml:onProperty rdf:resource="#hasParent"/> </daml:Restriction> </rdfs:subClassOf> </rdfs:Class>

  25. DAML basics cont.7 • Max, min cardinality (min default=0) <rdfs:Class rdf:about="#Person"> <rdfs:subClassOf> <daml:Restriction daml:maxcardinality="1"> <daml:onProperty rdf:resource="#hasSpouse"/> </daml:Restriction> </rdfs:subClassOf> </rdfs:Class>

  26. DAML basics cont.8 • UniqueProperty (cardinality=1), • Transitive <daml:UniqueProperty rdf:ID="hasMother"> <rdfs:subPropertyOf rdf:resource="#hasParent"/> <rdfs:range rdf:resource="#Female"/> </daml:UniqueProperty> <daml:TransitiveProperty rdf:ID="hasAncestor"> <rdfs:label>hasAncestor</rdfs:label> </daml:TransitiveProperty>

  27. DAML basics cont.9 • one of <rdf:Property rdf:ID="hasHeight"> <rdfs:range rdf:resource="#Height"/> </rdf:Property> <rdfs:Class rdf:ID="Height"> <daml:oneOf rdf:parseType="daml:collection"> <Height rdf:ID="short"/> <Height rdf:ID="medium"/> <Height rdf:ID="tall"/> </daml:oneOf> </rdfs:Class>

  28. DAML basics cont.10 • hasValue, intersectionOf <rdfs:Class rdf:ID="TallThing"> <daml:sameClassAs> <daml:Restriction> <daml:onProperty rdf:resource="#hasHeight"/> <daml:hasValue rdf:resource="#tall"/> </daml:Restriction> </daml:sameClassAs> </rdfs:Class> <rdfs:Class rdf:ID="TallMan"> <daml:intersectionOf rdf:parseType="daml:collection"> <rdfs:Class rdf:about="#TallThing"/> <rdfs:Class rdf:about="#Man"/> </daml:intersectionOf> </rdfs:Class>

  29. DAML basics cont.11 • instances <Person rdf:ID="Adam"> <rdfs:label>Adam</rdfs:label> <rdfs:comment>Adam is a person. </rdfs:comment> <hasHeight rdf:resource=“#medium”/> </Person>

More Related