topic maps and rdf(s)
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
CS3352
Topic Maps and RDF(S)Topic Maps and RDF(S)
CS3352
CS3352
Topic MapsTopic Maps From the document mark up community An 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
Extended to other forms of navigation aid: – The electronic equivalent of table of contents, glossaries,
thesauri, cross references The concepts or topics that underlie a set of
information objects exposed to those people or applications processing the information.
Seen by the document community as providing a new organising principle for information.
CS3352
Topic Map basicsTopic 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
Topic Maps: TopicsTopic 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
Topic Maps: OccurrencesTopic Maps: OccurrencesProvide 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
Topic Maps: AssociationsTopic Maps: Associations Allow more to be said about topics by
establishing relationships between topics. Associations between topics – bi-directional
– Tosca was written by Puccini, Rome is in Italy
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Topic Maps: other conceptsTopic 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
CS3352
CS3352
Topic Map Topic Map ImplementatioImplementatio
nnXML Topic Maps (XTM) 1.0XML 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
Topic MapsTopic 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
Topic Map Further ReadingTopic 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/
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Resource Description Resource Description Framework (RDF)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)
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RDF modelRDF model RDF “statements” consist of
resources (= nodes)which have properties which have values (= nodes, strings)
http://www.w3.org/TR/REC-rdf-syntax/
“Ora Lassila”
author
= subject= predicate= object
predicate(subject, object)
“http://www.w3.org/TR/REC-rdf-syntax/ has the author Ora Lassila”
resource
valueproperty
CS3352
Basic Model: ResourceBasic Model: Resource 1. A Resource is anything that can have a URI (and
optional anchor ids) includes all the Web's pages, as well 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/
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Basic Model: PropertyBasic 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
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Basic Model: StatementsBasic 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.
An example Statement is "The Author of http://www.cs.man.ac.uk/cs3362.html
is Carole Goble." The value can just be:
– a string, ( “Carole Goble“) or another resource ("The Home-Page of http://www.textuality.com/RDF/Why.html is http://www.textuality.com.“)
http://www.w3.org/TR/REC-rdf-syntax/
“Ora Lassila”author
CS3352
RDF model (example)RDF model (example)
http://www.w3.org/TR/REC-rdf-syntax/
“Ora Lassila”
dc:Creator
“1999-02-22”
dc:Date
“W3C”dc:Publisher
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Complex valuesComplex 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/
“Ora Lassila”
dc:Creator
p:EMailp:Name
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Complex values (continued)Complex values (continued) Corresponding triples
{ “http://www.w3.org/TR/PR-rdf-syntax/”, dc:Creator, x }{ x, p:Name, “Ora Lassila” }{ x, p:EMail, “[email protected]” }
http://www.w3.org/TR/REC-rdf-syntax/
“Ora Lassila”
dc:Creator
p:EMailp:Name
CS3352
ContainersContainers 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
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Containers (continued)Containers (continued)
http://www.w3.org/TR/REC-rdf-syntax
“Ora Lassila”
rdf:_1
rdf:Seq
dc:Creator
rdf:Type
“Ralph Swick”
rdf:_2
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Containers (continued)Containers (continued)
http://www.w3.org/TR/REC-rdf-syntax
“Ora Lassila”
dc:Creator
“Ralph Swick”
dc:Creator
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Containers (continued)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)
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Higher-order statementsHigher-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
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ReificationReification RDF is not really second-order But it does provide a built-in predicate
vocabulary for reificationhttp://www.w3.org/TR/REC-rdf-syntax “Ora Lassila”dc:Creator
“Library of Congress”
dc:Creator
• 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” }
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RDF modelRDF 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
RDF SyntaxRDF 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
RDF Syntax exampleRDF Syntax exampleOra 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
Problems with RDFProblems 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
RDF and RDF SchemaRDF 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
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RDF Schema ModelRDF Schema ModelProperty-centric
1. resource, class, subClassOf, type2. property, subPropertyOf3. 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
RDF Schema ModelRDF Schema Model
ClassMotorVehicle
Truck
PersonProperty
registeredTo
ownedByDomain
Range Resource
type
type
subClassOf
subClassOf
subClassOf
type
type type
CS3352
RDF Data ModelRDF Data Modelrdfs:Resource
rdfs:Class rdf:Property
RD
F/R
DFS
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appl:firstNameappl:marriedWith
appl:lastName
appl:Organisation
appl
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atahttp://www.foo.com/W.Smith
William Smith
appl:lastNameappl:firstName
http://www.foo.com/S.Smith
SmithSusan
appl:firstName appl:lastName
appl:marriedWith
subClassOfinstanceOf
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http://www.foo.com/W.Smith
William Smith
appl:lastNameappl:firstName
http://www.foo.com/S.Smith
SmithSusan
appl:firstName appl:lastName
appl:marriedWith
rdfs:Resource
rdfs:Class rdf:Property RD
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appl:Man appl:Woman appl:fatherInLaw appl:marriedWithappl:fatherOf
appl:Organisation o:secondComponento:firstComponent
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o:Partonomic-RolePropagation
CS3352
RDF and XMLRDF 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
RDF Schema syntax in XMLRDF 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>
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W3C project for shared web W3C project for shared web annotation using RDFannotation 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
Topic Maps vs RDF(S)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
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Layered LanguagesLayered Languages
XMLHTMLXHTML SMIL RDF(S)
PICS
Declarative Languages(OIL, DAML+OIL)
DC
The W3C hierarchy of languages:
CS3352
RDF, RDFSOILSemantic web
Building on StandardsBuilding on Standards
Html, HttpBrowsers
1990
DHTML, CSS, Javascript, CGISearch engines
XML, DTDs,
XLink
Static web
Dynamic web
Consistent web
1994 1996 1998 20001992
XSLTXML-QL
CS3352
RDF(S) Further ReadingRDF(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/