rdfs - university of maltastaff.um.edu.mt/cabe2/lectures/csa3210/slides/lecture5_rdfs.pdf ·...

RDFS

Charlie Abela

Department of Artificial Intelligence [email protected]

CSA 3210 RDF & RDFS © 2

Exercises: Header Definition

<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE rdf:RDF [

<!ENTITY rdf "http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <!ENTITY rdfs "http://www.w3.org/2000/01/rdf-schema#"> <!ENTITY xsd "http://www.w3.org/2001/XMLSchema#"> <!ENTITY books "http://www.booksonline.com/books#"> <!ENTITY authors “http://www.cs.um.edu.mt/authors#> <!ENTITY base “http://www.cs.um.edu.mt/library/>

]> <rdf:RDF

xmlns:rdf=“&rdf;” xmlns:rdfs=“&rdfs;” xmlns:xsd=“&xsd; xmlns:books=“&books;” xmlns:authors=“&authors;” xmlns:base=“&base;”>


RDF/XML Definitions/Graph View

n  The library is located in Bremen <rdf:Description rdf:about=“library”> <books:libraryLoc rdf:datatype=“&xsd;string”>Bremen</books:libraryLoc> </rdf:Description>


Graph View n The book with title “Artificial Intelligence” and ISBN 978-123458 is written by the author Henry Wise


RDF/XML Definitions II n  The book with title “Artificial Intelligence” and ISBN

978-123458 is written by the author Henry Wise <rdf:Description rdf:about="book012"> <rdf:type rdf:resource="&books;Book"/> <books:title rdf:datatype="&xsd;string">Artificial Intelligence </books:title> <books:isbn rdf:datatype="&xsd;string">ISBN 978123478</books:isbn> <books:author rdf:resource="#author12"/> </rdf:Description> <rdf:Description rdf:about="author12"> <books:authorName rdf:datatype="&xsd;string">HenryWise </books:authorName> </rdf:Description>


Graph View n The author William Start wrote the books with titles “Modern Web Services” and “Theory of Computation”


RDF/XML Definition

n  The author William Start wrote the books with titles “Modern Web Services” and “Theory of Computation”

<rdf:Description rdf:about="author13"> <rdf:type rdf:resource="&books;author"/> <books:authorName rdf:datatype="&xsd;string">William Start

</books:authorName> <books:authorOf rdf:parseType="Collection"> <rdf:Description rdf:about="#book103"/> <rdf:Description rdf:about="#book102"/> </books:authorOf>

</rdf:Description>


Moving up the layers


RDF Schema

n  Consider the following XML <author>Dan Brown</author> <journalist>John News</journalist> <magazine title=“Internet Computing”> <contributor>John Davies </contributor>

</magazine>

n  Use XPath to collect all authors: //author n  Result: “Dan Brown” n  Though XML is correct, it is semantically unsatisfactory

(result should contain also John News and John Davies) n  Need to define something of this sort:

q  Authors, journalists and contributors are all writers q  Only writers can contribute to a magazine


RDF Schema II

n  RDF makes no assumptions about any specific domain, nor does it define the semantics of such a domain

n  To define the terminology related to any domain a schema language such as RDF Schema can be used

n  Relation between RDF and RDF Schema is not the same as that between XML and XML Schema q  XML schema constraints the structure of XML documents q  RDFS defines the vocabulary used within an RDF data model

n  through RDFS its also possible to q  specify the properties that can be applied to an object q  specify the values that such properties can take q  declare relationships between objects


RDF Schema III

n  The user can describe any particular domain using: q  Classes and Properties: differentiate between individual objects

(or instances) and classes of object n  author: Dan Brown and class of authors n  restrict properties to apply to certain things

q  Only authors can contribute to certain magazines i.e. restrict the domain of contributors to a magazine as ranging only over authors

q  Class Hierarchies and Inheritance n  Classes of authors, writers, journalists, reporters, editors etc

q  authors, journalists and reporters are all writers (journalist is a subclass of writer)

q  Property Hierarchies n  E.g. the property “authorOf” is a subproperty of “contributesTo” n  However the converse may not necessarily be always true


Core Classes

n  rdfs:Resource, the class of all resources n  rdfs:Class, the class of all classes n  rdfs:Literal, the class of all literals

(strings) n  rdf:Property, the class of all properties. <rdfs:Class rdf:about=“Process”> <rdfs:comment>Represents the class of all processes</rdfs:comment>

</rdfs:Class>


Core Properties n  rdf:type, which relates a resource to its class

q  The resource is declared to be an instance of that class n  rdfs:subClassOf, which relates a class to one of its

superclasses q  All instances of a class are instances of its superclass

n  rdfs:subPropertyOf, relates a property to one of its superproperties <rdfs:Class rdf:ID=“SysProcess”> <rdfs:subClassOf rdf:resource=“#Process”/> </rdfs:Class> <rdf:Property rdf:ID=“authorOf”> <rdfs:subPropertyOf rdf:resource=“#contributeTo”/> <rdf:Property>


Core Properties (2)

n  rdfs:domain, which specifies the domain of a property P q  The class of those resources that may appear as subjects in a triple

with predicate P q  If the domain is not specified, then any resource can be the subject

n  rdfs:range, which specifies the range of a property P q  The class of those resources that may appear as values (of objects)

in a triple with predicate P <rdf:Property rdf:ID=“procName”> <rdfs:domain rdf:resource=“#Process”/> <rdfs:range rdf:range=“&xsd;string”/> </rdf:Property>


Example Literal

Contributor

Writer

Editor

Bookhas_name

has_name

subClassOf

subClassOf

authorOfhas_editor

Author

subClassOf

Journalist

subClassOf


RDFS Example <rdfs:Class rdf:ID=“Writer”/> <rdfs:Class rdf:ID=“Author"> <rdfs:comment>all authors that contribute to books</

rdfs:comment> <rdfs:subClassOf rdf:resource="#Writer"/> </rdfs:Class> <rdfs:Class rdf:ID=“Book"> <rdfs:comment>The class of books</rdfs:comment>

</rdfs:Class> <rdf:Property rdf:ID=“authorOf"> <rdfs:subPropertyOf rdf:resource="#contributeTo"/> <rdfs:domain rdf:resource=“#Writer”/> <rdfs:range rdf:resource=“#Book”/>

</rdf:Property>


RDFS Example II

<rdfs:Class rdf:about="#Author"> <rdfs:subClassOf rdf:resource="#Writer"/>

</rdfs:Class>

<rdf:Property rdf:ID=“phone"> <rdfs:domain rdf:resource="#Writer"/> <rdfs:range rdf:resource=“&xsd;Literal"/>

</rdf:Property>


Complete Example


Instance Example


Applications of RDF/S: FOAF

n  FOAF (Friend of a Friend) n  FOAF is a way of providing affiliation and other social

information about yourself n  Also a way of describing a network of friends and

others we know, in such a way that automated processes such as web bots can find this information and incorporate it with other FOAF files

n  The FOAF-a-matic is a web form and the submitted information is used to generate the RDF/XML for a specific FOAF file and add it to the FOAF network.


Foaf Example <foaf:Person rdf:ID="jhendler"><foaf:mbox_sha1sum>0b62d4242736e64be6138547c79a811b3e82fd52</foaf:mbox_sha1sum><foaf:firstName>Jim</foaf:firstName><foaf:surname>Hendler</foaf:surname><foaf:name>Jim Hendler</foaf:name><foaf:title>Tetherless World Constellation Chair</foaf:title>

<foaf:homepage rdf:resource="http://trust.mindswap.org/cgi-bin/FilmTrust/foaf.cgi?user=jhendler"/><foaf:homepage rdf:resource="http://www.cs.umd.edu/~hendler"/><foaf:depiction rdf:resource="http://www.semanticgrid.org/q-iantbljim.jpg"/>

<foaf:workplaceHomepage rdf:resource="http://owl.mindswap.org"/><foaf:img rdf:resource="http://www.cs.umd.edu/~hendler/hendler.gif"/><foaf:depiction rdf:resource="http://www.cs.umd.edu/~hendler/hendler.gif"/><foaf:nick>jhendler</foaf:nick>

<foaf:knows><foaf:Person rdf:about="http://trust.mindswap.org/cgi-bin/FilmTrust/foaf.cgi?user=golbeck#golbeck"><rdfs:seeAlso rdf:resource="http://trust.mindswap.org/cgi-bin/FilmTrust/foaf.cgi?user=golbeck"/><foaf:nick>golbeck</foaf:nick>

</foaf:Person></foaf:knows>

<foaf:knows><foaf:Person rdf:about="http://trust.mindswap.org/cgi-bin/FilmTrust/foaf.cgi?user=finin#finin"><rdfs:seeAlso rdf:resource="http://trust.mindswap.org/cgi-bin/FilmTrust/foaf.cgi?user=finin"/><foaf:nick>finin</foaf:nick>

</foaf:Person></foaf:knows>


Photos of People I Know

FOAF

<foaf:knows><foaf:Person rdf:about="http://www.JohnGrech.org/john#john"/>

</foaf:knows><foaf:knows>

<foaf:Person rdf:about="http://www.PeterBorg/pietru#pietru"/></foaf:knows>

JohnFOAF

PeterFOAF

PersonalisedView

Photosfrom friends'

websites

PEA


Applications of RDF/S: RDFHomepage

n  Creates personal homepages based on your RDF data. n  Takes the information in Bibtex, FOAF files, etc. and

automatically creates an RDFHomepage. n  The generated HTML code is very general, and allows

quick and easy page-redesigning using CSS. n  RDFHomepage is written in PHP and uses the system

to generate PHP classes based on RDF class definitions


RDFHomepage: Social Network Researchers


RDF Tools

n  RDF Store: stores RDF models in relational dbs (persistent storage) q  Jena can be hooked with MySQL, PostgreSQL or Oracle db

n  RDF validator: validates RDF and presents different views (triples and dg) of result

n  RDF Editors: q  Protégé: http://protege.stanford.edu/ q  Oiled: http://oiled.man.ac.uk/ q  SWOOP: http://www.mindswap.org/2004/SWOOP/

n  RDF visualiser q  RDF Viz (visualises graphs)

n  Search for schemas: q  SWOOGLE: http://swoogle.umbc.edu/


Further Information

n  Semantic Web Primer, Chapter 3 n  RDF Primer, E. Miller

q  http://www.w3.org/TR/rdf-primer/

n  RDF tutorial examples q  http://www.zvon.org/xxl/RDFTutorial/General/contents.html

n  The Semantic Web: roles of XML and RDF, Stefan Decker, q  http://www.ontoknowledge.org/oil/downl/IEEE00.pdf

n  Jena RDF tutorial, q  http://jena.sourceforge.net/documentation.html


Exercise

n  Create an RDFS vocabulary for this scenario n  Create an instance file with an author that has

published 3 different publications. You can add relevant properties to the basic concepts

Publication

ArticleConference_

Paper Book

Copyrights Author

xsd:string

has_namehas_phone

subClassOfsubClassOf subClassOf

copyrightedBy publishes

xsd:string

copyRightYear

xsd:string

copyRightContent

xsd:string

ISBN

xsd:string

publisherName

xsd:string

xsd:string

has_title


Next Lecture

n  Introduction to Description Logics q  basis for Semantic Web languages

n  Ontologies q  Definition q  Building q  Use


Namespaces for shorter serialisation n  Writing URIs results in very long lines. n  For convenience we use a shorthand of writing triples. n  The XML qualified name without angle brackets <> is

used as abbreviation for the full URI reference. n  A QName contains a prefix that has been assigned to a

namespace URI, followed by a colon, and then a local name.

n  The full URI is formed from the QName by appending the local name to the namespace URI assigned to the prefix.

n  So, for example, if the QName prefix foo is assigned to the namespace URI http://example.org/somewhere/, then the QName foo:bar is shorthand for the URIref q  http://example.org/somewhere/bar.


Namespaces used

n  prefix rdf:, namespace URI: http://www.w3.org/1999/02/22-rdf-syntax-ns#

n  prefix books:, namespace URI: http://www.booksInfo.com/books#”

n  prefix xsd:, namespace URI: http://www.w3.org/2001/XMLSchema#

n  prefix authors:, namespace URI: http://www.authorsInfo.org/authors#”

n  prefix base:, namespace URI: http://www.bookstore.com/books

rdfs - university of maltastaff.um.edu.mt/cabe2/lectures/csa3210/slides/lecture5_rdfs.pdf ·...

Documents