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Topic Maps and RDF(S)

Topic Maps and RDF(S). CS3352. Topic Maps. From the document mark up community A n ISO Standard (ISO13250) describing knowledge structures. Aim: to enable information resources to be classified and navigated in a consistent manner by representing knowledge structures for indexes

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Topic Maps and RDF(S)

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  1. Topic Maps and RDF(S) CS3352 CS3352

  2. Topic Maps • From the document mark up community • An ISO Standard (ISO13250) describing knowledge structures. • Aim: to enable information resources to beclassified and navigated in a consistentmanner by representing knowledge structures for indexes • Extended to other forms of navigation aid: • The electronic equivalent of table of contents, glossaries, thesauri, cross references • The concepts or topicsthat underlie a set of information objects exposed to those people or applicationsprocessing the information. • Seen by the document community as providing a new organising principle for information. CS3352

  3. Topic Map basics • Based on Semantic Nets and Indexes • Implemented using XML and XLL (XLink, XPointer) • Topics, Associations and Occurrences • typed to form groups – • types are defined in the standard as topics • Topic - Tosca is of type opera • Occurrence - Picture X plays role of portrait • Association - Written-by is a type of association • Topics and Occurrences play roles in relationships CS3352

  4. Topic Maps: Topics • Topics – a resource surrogate or proxies for Subjects • Tosca, Madam Butterfly, Rome, Puccini, Italy • Represent any concept helpful to the meaningful description of information objects. CS3352

  5. Topic Maps: Occurrences Provide a route between a topic and an information object. Occurrences - addressable information resources that are linked to the topic – usually electronic • Picture, commentary, article etc Occurrences are outside the topic map document and are pointed to by the topic (using XLL – XLink and XPointer) A layer of topics and a layer of occurrences CS3352

  6. Topic Maps: Associations • Allow more to be said about topics byestablishing relationships between topics. • Associations between topics – bi-directional • Tosca was written by Puccini, Rome is in Italy CS3352

  7. Topic Maps: other concepts • Scope and Themes: • Used to describe the limits of the validity of a topic characteristic assignment. I.e. provides CONTEXT • Topics can have different names for different scopes • Facets: • Provide a mechanism for assigning properties to groups of information objects. E.g. language, security • Subject descriptors: • Establishing subject identity between topics within and across topic maps, e.g. when merging them. • Italia and Italy refer to the same subject. • Activity to develop directories of public subjects CS3352

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  10. Topic Map ImplementationXML Topic Maps (XTM) 1.0 <topicmap topic="simpletm"> <topic id="defocc" identity="net.ontopia.topicmaps.psd.iso13250.occurrence-type.default"> <topic id="produces"> <topname> <basename>producer of</basename> <sortname>~producer of</sortname> </topname> <topname scope="product"> <basename>product of</basename> <sortname>~product of</sortname> </topname> </topic> <topic id="simpletm"> <topname> <basename>Simple topic map</basename> </topname> <occurs type="website" href="http://www.ontopia.net/topicmaps/examples/ontopia/simple.htm"/> </topic> <assoc type="produces"> <assocrl type="vendor" href="ontopia"/> <assocrl type="product" href="oks"/> </assoc> </topicmap> CS3352

  11. Topic Maps • Each map is self-describing, carrying its own ontology defined as a topic map • Topic maps also used for defining control information • Work started on • schema language • TQML – query language • Upper topic model • XML Topic Maps (XTM) 1.0 • an abstract model and XML grammar for interchanging Web-based topic maps, written by the members of the TopicMaps.Org Authoring Group. • Semantic Networks circa 1985? • What happened to the last 20 years of knowledge representation? • Scale? Change? Semantics? Rigour? Inference? CS3352

  12. Topic Map Further Reading • http://www.topicmaps.org/ • http://www.topicmaps.com/ • http://www.ontopia.net/topicmaps/learn_more.html • Commercial examples using topic maps and XLink: http://www.empolis.co.uk/products/ CS3352

  13. Resource Description Framework (RDF) • W3C metadata technology • A model for metadata for describing resources • RDF is a data model • the model is domain-neutral, application-neutral • the model can be viewed as directed, labeled graphs or as an object-oriented model (object/attribute/value) • Makes no assumptions about a particular application domain • Doesn’t define a priori the semantics of any application domain • The specification provides an encoding (in XML) of the model • The syntactic details are secondary, they are largely handled by using XML (RDF defines a convention of XML usage) CS3352

  14. RDF model • RDF “statements” consist of resources (= nodes)which have properties which have values (= nodes, strings) = subject= predicate= object predicate(subject, object) resource value property “http://www.w3.org/TR/REC-rdf-syntax/ has the author Ora Lassila” http://www.w3.org/TR/REC-rdf-syntax/ author “Ora Lassila” CS3352

  15. Basic Model: Resource • 1. A Resource is anything that can have a URI (and optional anchor ids) • includes all the Web's pages, aswell as individual elements of an XML document. • E.g. a document whose URL is http://www.textuality.com/RDF/Why.html http://www.w3.org/TR/REC-rdf-syntax/ CS3352

  16. Basic Model: Property • A Property is a specific aspect, characteristic, attribute or relation to describe a resource. • Can be used as a property – a property needs to be a resource so that it can have its own properties. http://www.w3.org/TR/REC-rdf-syntax/ author CS3352

  17. Basic Model: Statements • A Statement consists of the combination of a Resource, a Property, and a value.These parts are known as the 'subject', 'predicate' and 'object' of a Statement. • Anexample Statement is • "The Author of http://www.cs.man.ac.uk/cs3362.html is Carole Goble." • The value can justbe: • a string, ( “Carole Goble“) oranotherresource ("The Home-Page ofhttp://www.textuality.com/RDF/Why.html ishttp://www.textuality.com.“) http://www.w3.org/TR/REC-rdf-syntax/ author “Ora Lassila” CS3352

  18. RDF model (example) “W3C” dc:Publisher http://www.w3.org/TR/REC-rdf-syntax/ dc:Creator dc:Date “Ora Lassila” “1999-02-22” CS3352

  19. Complex values • A graph node (corresponding to a resource) also can be the value of a property • arbitrarily complex tree and graph structures are possible • syntactically, values can be embedded (i.e. lexically in-line) or referenced (linked) http://www.w3.org/TR/REC-rdf-syntax/ dc:Creator “Ora Lassila” p:Name p:EMail “ora.lassila@nokia.com” CS3352

  20. Complex values (continued) • Corresponding triples { “http://www.w3.org/TR/PR-rdf-syntax/”, dc:Creator, x } { x, p:Name, “Ora Lassila” } { x, p:EMail, “ora.lassila@nokia.com” } http://www.w3.org/TR/REC-rdf-syntax/ dc:Creator “Ora Lassila” p:Name p:EMail “ora.lassila@nokia.com” CS3352

  21. Containers • Containers are collections • they allow grouping of resources (or literal values) • It is possible to make statements about the container (as a whole) or about its members individually • Different types of containers exist • bag - unordered collection • seq - ordered collection (= “sequence”) • alt - represents alternatives • It is also possible to create collections based on URI patterns • for example, all files in a particular web site • Duplicate values are permitted • there is no mechanism to enforce unique value constraints CS3352

  22. Containers (continued) http://www.w3.org/TR/REC-rdf-syntax dc:Creator rdf:Type rdf:Seq rdf:_1 rdf:_2 “Ora Lassila” “Ralph Swick” CS3352

  23. Containers (continued) http://www.w3.org/TR/REC-rdf-syntax dc:Creator dc:Creator “Ora Lassila” “Ralph Swick” CS3352

  24. Containers (continued) • Triples from the first example: • { “http://www.w3.org/TR/REC-rdf-syntax”, dc:Creator, x } • { x, rdf:_1, “Ora Lassila” } • { x, rdf:_2, “Ralph Swick” } • { x, rdf:type, rdf:Seq } • Triples from the second example: • { “http://www.w3.org/TR/REC-rdf-syntax”, dc:Creator, “Ora Lassila” } • { “http://www.w3.org/TR/REC-rdf-syntax”, dc:Creator, “Ralph Swick” } • Syntactic shorthand provided (much like HTML lists) CS3352

  25. Higher-order statements • One can make RDF statements about other RDF statements • example: “Ralph believes that the web contains one billion documents” • Higher-order statements • allow us to express beliefs (and other modalities) • are important for trust models, digital signatures,etc. • also: metadata about metadata • are represented by modeling RDF in RDF itself CS3352

  26. dc:Creator http://www.w3.org/TR/REC-rdf-syntax “Ora Lassila” dc:Creator “Library of Congress” Reification • RDF is not really second-order • But it does provide a built-in predicate vocabulary for reification • The dotted box corresponds to the following statements • { x,rdf:predicate, “dc:creator” } • { x, rdf:subject, “http://www.w3.org/TR/RED-rdf-syntax } • { x, rdf:object, “Ora Lassila” } • { x, rdf:type, “rdf:statement” } CS3352

  27. RDF model • Graphs can be represented as relational “triples” • { “http://www.w3.org/TR/REC-rdf-syntax/”, author, “Ora Lassila” } • Any arc in a graph corresponds to one triple, consisting of the arc label itself and the two endpoints • When searching, this is useful only if we know what the meaning of “author” is • e.g., “find all documents where the author is Ora Lassila” • new triple { “http://www.w3.org/TR/REC-rdf-syntax/”, dc:Creator, “Ora Lassila” } • “author” replaced by a label which is uniquely qualified (using the XML namespace mechanism) • Drawn from a consensually pre-established vocabulary CS3352

  28. RDF Syntax • RDF Model and Syntax specification defines a convention of XML usage to “serialize” RDF • Most of the trouble people have had understanding RDF is probably caused by the syntax • The syntax was “designed by a committee”) • Lots of attention diverted onto abbreviated syntax • redesign of the syntax is possible at some point CS3352

  29. RDF Syntax example Ora Lassila is the creator of the resource http://www.w3.org/Home/Lassila. <?xml version="1.0"?> <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> CS3352

  30. Problems with RDF • Syntax is hard • Fixable but off-putting • Modelling is difficult • Confused simplicity with simple-minded • Confused generality with simplicity • E.g. Quantification? CS3352

  31. RDF and RDF Schema • RDF a small set of modelling primitives + syntax • RDF does not commit to a domain vocabulary • RDF Schema -- RDF(S) • Extended set of modeling primitives • Define a domain vocabulary for RDF • Organise this vocabulary in a typed hierarchy • BUT expressive inadequacy and poorly defined semantics • RDFS is the framework for a vocabulary • RDF schema provides an extensible, object-oriented type system • Schema definitions are expressed in RDF itself CS3352

  32. RDF Schema Model Property-centric • resource, class, subClassOf, type • property, subPropertyOf • domain, range, constraintResource, constraintProperty a new class can be defined by extending an existing class • extension reuses (and thus shares) existing definition(s) • a class can have multiple superclasses schema definitions can include constraints which express validation conditions • domain constraints link properties with classes • range constraints limit property values • “hook” for new constraints CS3352

  33. RDF Schema Model Resource Range subClassOf Person type Property Class type type MotorVehicle registeredTo type type subClassOf subClassOf Domain Truck ownedBy CS3352

  34. RDF Data Model subClassOf rdfs:Resource instanceOf RDF/RDFS layer and namespace rdfs:Class rdf:Property appl:Organisation appl:Person appl:marriedWith appl:firstName application specific schema and namespace appl:Man appl:Woman appl:lastName appl:marriedWith http://www.foo.com/W.Smith http://www.foo.com/S.Smith application specificactual data appl:firstName appl:lastName appl:firstName appl:lastName William Smith Susan Smith CS3352

  35. subClassOf rdfs:Resource instanceOf RDF/RDFSlayer and namespace rdfs:Class rdf:Property o:Partition o:Relation o:Composition o:Partonomic- RolePropagation ontology meta layerand namespace o:isInverseRelationOf o:PartOfRel o:Asymmetric o:Reflexive o:Symmetric o:Transitive o:Irreflexive appl:Organisation o:secondComponent o:firstComponent appl:Person o:composee Application-specific schema and namespace appl:Man appl:Woman appl:fatherInLaw appl:fatherOf appl:marriedWith appl:marriedWith Application- specificactual data http://www.foo.com/W.Smith http://www.foo.com/S.Smith appl:lastName appl:lastName appl:firstName appl:firstName William Smith Susan Smith CS3352

  36. RDF and XML • RDF data model is an abstract, conceptual layer independent of XML • consequently, XML is a transfer syntax for RDF, not a component of RDF • RDF data might never occur in XML form • it might reside, for example, in an RDB • XML relieves us of syntactic details when transporting RDF CS3352

  37. RDF Schema syntax in XML <rdf:Description ID="MotorVehicle"> <rdf:type resource="http://www.w3.org/...#Class"/> <rdfs:subClassOf rdf:resource="http://www.w3.org/...#Resource"/> </rdf:Description> <rdf:Description ID="Truck"> <rdf:type resource="http://www.w3.org/...#Class"/> <rdfs:subClassOf rdf:resource="#MotorVehicle"/> </rdf:Description> <rdf:Description ID="registeredTo"> <rdf:type resource="http://www.w3.org/...#Property"/> <rdfs:domain rdf:resource="#MotorVehicle"/> <rdfs:range rdf:resource="#Person"/> </rdf:Description> <rdf:Description ID=”ownedBy"> <rdf:type resource="http://www.w3.org/...#Property"/> <rdfs:subPropertyOf rdf:resource="#registeredTo"/> </rdf:Description> CS3352

  38. W3C project for shared web annotation using RDF • Comments, notes, explanations, or other types of external remarks that can be attached to any Web document or a selected part of the document without actually needing to touch the document. • Uses an RDF based annotation schema for describing annotations as metadata and XPointer for locating the annotations in the annotated document. • First client implementation of Annotea is an editor/browser CS3352

  39. Topic Maps vs RDF(S) • Both are weak • Inexpressive • No semantics • Reinventing wheels not terribly effectively • Slightly different perspectives • Topic Maps – topic centric • RDF(S) – property centric • Topic maps have the notion of “aboutness” lacking in RDF, which has the notion of “instance” • Both use XML as a carrier syntax • A religious war CS3352

  40. Layered Languages The W3C hierarchy of languages: Declarative Languages (OIL, DAML+OIL) DC PICS SMIL RDF(S) XHTML HTML XML CS3352

  41. Building on Standards OIL Semantic web RDF, RDFS XLink Consistent web XML, DTDs, XML-QL XSLT Dynamic web DHTML, CSS, Javascript, CGI Search engines Static web Browsers Html, Http 1990 1992 1994 1996 1998 2000 CS3352

  42. RDF(S) Further Reading • Tutorials • http://www.zvon.org/xxl/RDFTutorial/General/book.html • http://www.xml.com/pub/a/98/06/rdf.html • RDF Resource collection • http://www.ilrt.bristol.ac.uk/discovery/rdf/resources/ • Why RDF is different to XML • http://www.w3.org/DesignIssues/RDF-XML.html • W3C • http://www.w3.org/RDF/ CS3352

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