Information Retrieval 2

Transkript

1 Information Retrieval 2 10 November 2010 Martin Wolpers

2 Heute und die nächsten Male Administratives Klausur , 13 15:00 Uhr Klausureinsicht Do Fr fällt aus, sonst nicht (hoffentlich!) Problemstellung: Das MACE System Lösungsansatz Zentrales Repository, Lucene Index Alternativer Lösungsansatz Semantic Web, RDF und OWL Das Gute und das Schlechte

3 Alternativer Lösungsansatz Problem mit gewählter Lösung Schema-basierte Verknüpfung von Learning Resources Daraus resultierend hoher Programmieraufwand für die Navigation in Learning Resources Alternative: Graph der Learning Resources Graph-Algorithmen für IR anwendbar Semantische Beschreibung der Learning Resources Explizite Beziehungen zwischen Learning Resources Hier: Semantic Web (basierend auf der Vorlesung Semantic Web von Prof. Dr. Nicola Henze, Universität Hannover

4 Reifikation man kann darüber sprechen <rdf:description rdf:about= <dc:author>martin Wolpers</dc:author> </rdf:description> Ist auch <rdf:statement rdf:about= statementabouthttp:// tml"> <rdf:subject rdf:resource=" <rdf:predicate rdf:resource="dc:author"> <rdf:object rdf:resource= Martin Wolpers"> </rdf:statement>

5 Reifikation Beispiel 2 Aussage 1: hat den Autoren Martin Wolpers Aussage 2: Klaus sagt, daß den Autoren Martin Wolpers hat. Unproblematisch: <rdf:description rdf:about= <dc:author>martin Wolpers</dc:author> </rdf:description> Aber wie über Aussage 1 die Aussage 2 formulieren? Dafür wird Reifikation benötigt!

6 Reifikation Beispiel 2 Reifikation von Aussage 1: (Achtung, vereinfachte Notation N3) statementaboutaussage1 rdf:type rdf:statement statementaboutaussage1 rdf:subject statementaboutaussage1 rdf:predicate dc:author statementaboutaussage1 rdf:object Martin Wolpers Aussage 2 hinzufügen: statementaboutaussage1 mynamespace:sagt person:klaus

7 Alternative Formulierung zu Reifikation Einsatz von RDF ID: <rdf:description rdf:id= <dc:author rdf:id= triple1 >Martin Wolpers</dc:author> </rdf:description> <rdf:description rdf:about="#triple1"> <mynamespace:sagt rdf:resource= person:klaus /> </rdf:description>

8 Allgemeine Datentypen rdf:datatype zur Instanzierung aller Datentypen Bspw: String: Consequence: RDF allows the use of any externally denoted data typing scheme (Practically, most widely used data typing schemes are the ones denoted by XML Schema)

9 N-ary Relationen RDF allows for binary properties only! Ein Schachspiel: X ist Schiedsrichter für ein Schachspiel zwischen den Spielern Y und Z. Quadruple: Schiedsrichter(X,Y,Z) In RDF ref(chessgame,x) player1(chessgame,y) player2(chessgame,z)

10 Container Elements Typical application of containers: The representation of predicates with more than two arguments. rdf:bag unordered may contain multiple occurrences rdf:seq ordered may contain multiple occurrences rdf:alt a set of alternatives Content of container elements are named rdf:_1, rdf:_2,.. Container elements can have an optional ID attribute

11 Beispiele für Container <rdf:bag rdf:id= IR courses"> <rdf:_1:rdf:resource= Inf Ret 1"/> <rdf:_2:rdf:resource= Inf Ret 2"/> </rdf:bag> <rdf:alt> <rdf:_1:rdf:resource= Martin Wolpers"/> <rdf:_2:rdf:resource= Stefaan Ternier"/> </rdf:alt> Note: There is no possibility "to close" the container, to say: "these are all elements" RDF is a graph, so: there is no way to exclude the possibility that there is another graph somewhere that describes additional members

12 Collections Collections: describe groups containing only the specified members Realized via a predefined collection vocabulary consisting of the predefined types: rdf:list, rdf:first, rdf:rest, rdf:nil CIT 2112 is exclusively taught by teachers ,949352, : <rdf:description rdf:about="cit2112"> <uni:istaughtby> <rdf:list> <rdf:first><rdf:description rdf:about="949111"/></rdf:first> <rdf:rest> <rdf:list> <rdf:first><rdf:description rdf:about="949352"/></rdf:first> <rdf:rest> <rdf:list> <rdf:first><rdf:description rdf:about="949318"/></rdf:first> <rdf:rest><rdf:description rdf:about="&rdf;nil"/></rdf:rest> </rdf:list> </rdf:rest> </rdf:list> </rdf:rest> </rdf:list> </uni:istaughtby> </rdf:description>

13 Machen wir es uns einfacher - Abbreviation Abbreviation: Using the rdf:parsetype attribute: <rdf:description rdf:about="cit2112"> <uni:istaughtby rdf:parsetype="collection"> <rdf:description rdf:about="949111"/> <rdf:description rdf:about="949352"/> <rdf:description rdf:about="949318"/> </uni:istaughtby> </rdf:description> Three Rules 1. The namespace can be abbreviated with "&namespace name; 2. Childless property elements within description elements may be replaced by XML attributes (as in XML) 3. For description elements with a typing element we can use the name specified in the rdf:type element instead of rdf:description

14 Mal sehen, was das bringt <rdf:rdf xmlns:rdf=" xmlns:uni=" <rdf:description rdf:id="cit1111"> <rdf:type rdf:resource=" <uni:coursename>discrete Mathematics</uni:courseName> <uni:istaughtby rdf:resource="#949318"> </rdf:description> is equivalent to (according to rule 1) <rdf:rdf xmlns:rdf=" xmlns:uni=" <rdf:description rdf:id="cit1111"> <rdf:type rdf:resource="&uni;course"/> <uni:coursename>discrete Mathematics</uni:courseName> <uni:istaughtby rdf:resource="#949318"> </rdf:description>

15 Und weiter geht s is equivalent to (according to rule 1) <rdf:rdf xmlns:rdf=" xmlns:uni=" <rdf:description rdf:id="cit1111"> <rdf:type rdf:resource="&uni;course"/> <uni:coursename>discrete Mathematics</uni:courseName> <uni:istaughtby rdf:resource="#949318"> </rdf:description> is equivalent to (according to rule 2) <rdf:rdf xmlns:rdf=" xmlns:uni=" <rdf:description rdf:about="cit1111 uni:coursename="discrete Mathematics"> <rdf:type rdf:resource="&uni;course"/> <uni:istaughtby rdf:resource="#949318"> </rdf:description>

16 Und schlussendlich is equivalent to (according to rule 2) <rdf:rdf xmlns:rdf=" xmlns:uni=" <rdf:description rdf:about="cit1111 uni:coursename="discrete Mathematics"> <rdf:type rdf:resource="&uni;course"/> <uni:istaughtby rdf:resource="#949318"> </rdf:description> and is equivalent to (according to rule 3) <rdf:rdf xmlns:rdf=" xmlns:uni=" <uni:course rdf:about="cit1111 uni:coursename="discrete Mathematics"> <uni:istaughtby rdf:resource="#949318"> </uni:course>

17 RDF Schema RDF offers universal languages that lets users describe resources independent from any application domain BUT No means to describe a data schema (some call it semantics) Hence, introducing RDF Schema! Used to describe the semantics of a given domain!

18 Elements of RDF Schema Class Class Blaupause der zu beschreibenden Elemente Typisierung gleicher Elemente Subclass Of Vererbungsrelation zw. Klassen Hierarchie von Klassen Vererbung der Eigenschaften Mehrere Superklassen

19 Elements of RDF Schema Property Property Eigenschaft eines Elements Restriktion des Wertebereichs der Eigenschaft (range of a property) Properties werden GLOBAL angegeben Beachte Unterschied Frame-basierte und Property-basierte Logiken! Range und Domain Restriktionen SubPropertyOf Hierarchisierung von Properties (besonderes Constraint) Nicht invers: "is taught by" is a subproperty of "involves": If a course c is taught by an academic staff member a, then c also involves a. The converse is not necessarily true: A tutor is involved in a course, but does not teach it.

20 RDF Beispiel (taken from semweb primer)

21 RDFS Elemente RDFS: Core Classes rdfs:resource The class of all resources rdfs:class The class of all classes rdfs:literal The class of all literals (strings) Currently: only data type of RDF/RDFS is string rdf:property The class of all properties rdf:statement The class of all reied statements RDFS: Core Properties rdf:type relates a resource to its class (the resource is declared to be an instance of that class) rdfs:subclassof relates a class to one of its superclasses; all instances of a class are instances of its superclass rdfs:subpropertyof relates a property to one of its superproperties rdfs:subclassof and rdfs:subpropertyof are transitive.

22 RDF Property restriction rdfs:domain species the domain of a property - the class of resources that may appear as subjects rdfs:range species the range of a property - the class of resources that may appear as values <rdf:property rdf:id="phone"> <rdfs:domain rdf:resource="#staffmember"/> <rdfs:range rdf:resource="&rdf;literal"/> </rdf:property>

23 Constraints rdfs:constraintresource the class of all constraints rdfs:constraintproperty species all properties that define constraints. It has only two instances: rdfs:domain and rdfs:range. It is defined to be a subclass of rdfs:constraintresource and rdf:property Properties for Reification rdf:subject relates a reified statement to its subject rdf:predicate relates a reified statement to its predicate rdf:object relates a reified statement to its object

24 Container and Utilities Container rdf:bag rdf:seq rdf:alt rdfs:container the superclass of all container classes, especially of Bag, Alt, Seq. Utility Properties rdfs:seealso relates a resource to another resource that explains it rdfs:isdenedby subproperty of rdfs:seealso, relates a resource to the resource where its denition is found rdfs:comment Comments rdfs:label "human-friendly" label (name); also nice for naming the nodes in a graphical representation of RDF

25 Übung zu RDF Erproben, wie RDF funktioniert. Erstellen Sie die RDF Darstellung des Sachverhalts im Bild. Beschreiben Sie diesen Kurs auszugsweise mithilfe des von Ihnen erstellten RDF Schemas.

26 Aufgabe

27 Tools zu RDF, OWL, etc. Gute Zusammenstellung: Editor: Protégé RDF Validator:

28 Lösung 1 Modellierung des Schemas <rdf:rdf xmlns:rdf=" xmlns:rdfs=" <rdfs:class rdf:id="person"></rdfs:class> <rdfs:class rdf:id="student"> <rdfs:subclassof rdf:resource="#person"/> </rdfs:class> <rdfs:class rdf:id="teacher"> <rdfs:subclassof rdf:resource="#person"/> </rdfs:class> <rdfs:class rdf:id="course"></rdfs:class> <rdf:property rdf:id="has_teacher"> <rdfs:domain rdf:resource="#course"/> <rdfs:range rdf:resource="#teacher"/> </rdf:property>

29 Lösung 2 Modellierung des Schemas <rdf:property rdf:id="has_students"> <rdfs:domain rdf:resource="#course"/> <rdfs:range rdf:resource="#student"/> </rdf:property> <rdf:property rdf:id="has_name"> <rdfs:domain> <rdf:bag> <rdf:_1:rdf:resource="#person"/> <rdf:_2:rdf:resource="#course"/> </rdf:bag> </rdfs:domain> <rdfs:range rdf:resource=" </rdf:property> </rdf:rdf>

30 Lösung 3 Instanzierung des Schemas <rdf:rdf xmlns:rdf=" xmlns=" <Course rdf:id= IR2"> <has_name>information Retrieval 2</has_name> <has_teacher> <Teacher rdf:id= mw"> <has_name>martin Wolpers</has_name></Teacher> </has_teacher> <has_students> <rdf:seq> <rdf:li> <Student rdf:id= kk"> <has_name>klaus Katz</has_name> </Student> </rdf:li>

31 Lösung 4 Instanzierung des Schemas <rdf:li> <Student rdf:id= el"> <has_name>effie Lass</has_name> </Student> </rdf:li> </rdf:seq> </has_students> </Course> </rdf:rdf>

32 OWL OWL Primer Chapter 4, Section 1 from A Semantic Web Primer" by G. Antoniou, F. v. Harmelen Slides 1-58