02 - semantic web technologien - uri and rdf

Semantic Web Technologies

LectureDr. Harald Sack

Hasso-Plattner-Institut für IT Systems EngineeringUniversity of Potsdam

Winter Semester 2012/13

Lecture Blog: http://semweb2013.blogspot.com/This file is licensed under the Creative Commons Attribution-NonCommercial 3.0 (CC BY-NC 3.0)

Dienstag, 23. Oktober 12

Semantic Web Technologies , Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

2 1. Introduction 2. Semantic Web - Basic Architecture

Languages of the Semantic Web - Part 1

3. Knowledge Representation and LogicsLanguages of the Semantic Web - Part 2

4. Applications in the ,Web of Data‘

Semantic Web Technologies Content

2. Semantic Web - Basic ArchitectureLanguages of the Semantic Web - Part 1

2. Semantic Web Basic ArchitectureThe Languages of the Semantic Web - Part 1

• Uniform Resource Identifier - URI• Recapitulation: XML and XMLSchema• Resource Description Framework - RDF

• RDF Schema• How Do We Get Semantics into WWW?

• µFormats, schema.org, RDFa and GRDDL• Query Language SPARQL• Why RDF(S) is not enough

What is this?

What`s the difference?

Semiotic Triangle

Symbol Objectstands for

Ogden, Richards, Semiotic Triangle, 1923

„apple“

symbolizes refers to

Concept

shared concept

Uniform

Resource

Identifier

□ different types of resource identifiers all constructed according to a uniform schema

□ whatever may be identified via URI

□ to distinguish one resource from another

The Designator in the Web

Uniform Resource Identifier ■ A Uniform Resource Identifier (URI) defines a simple and extensible schema

for worldwide unique identification of abstract or physical resources (RFC 3986).

■ Resource can be every object with a clear identity (according to the context of the application) □ as e.g., web pages, books, locations, persons, relations among

objects, abstract concepts, etc.■ The concept of URI is already established in various domains, as e.g., □ the Web (URL, PRN, pURL), □ Books and publications (ISBN, ISSN), □ Digital Object Identifier (DOI)

URI, Resource and Representation

http://www.tour-eiffel.fr/index.htmlURI

Eiffel Tower

Resource

Metadata: Content-type: text/htmlData:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Le site officiel de la Tour Eiffel</title> ...</html>

representation

identifies

represents (stands for)

Representation and Presentation

11Metadata: Content-type: text/htmlData:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Le site officiel de la Tour Eiffel</title> ...</html>

Representation

defines

Presentation

HTTP Request / Response

User clicks

Browser sendsHTTP Request

GET http://www.tour-eiffel.fr/index.html HTTP/1.1Host: www.tour-eiffel.frAccept: text/html

Browser sends HTTP RequestGET http://www.tour-eiffel.fr/index.html HTTP/1.1Host: www.tour-eiffel.frAccept: text/html

Web Server ofwww.tour-eiffel.fr

Web Server processes request

Web Server sends HTTP ResponseHTTP/1.1 200 OKContent-Length: 3134Content-Type: text/html; charset=utf-8

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Le site officiel de la Tour Eiffel</title> ...</html>

Browser interprets representation and displays presentation

HTTP Request / Response

Designator and Designatum

The web page describes (designates) the Eiffel Tower

Designator

Designatum

The Eiffel Tower is described (designated) by the web page

2. Semantic Web Basisarchitektur2.1 Uniform Resource Identifier - URI

Bezeichner und Bezeichnetes

René Magritte: La trahison des images (1928)

Designator and Designatum

W3C: Architecture of the World Wide Web, Volume One

□A resource can be described (designated) via Metadata □ Even if the resource itself cannot be delivered from the

web server, probably its representation might be available that describes the resource sufficiently.

The distinguishing characteristic of [information] resources is that all of their essential characteristics can be conveyed in a message.

Metadata

Metadaten

Metadata

• „Metadata are data that contain information about other data“ and „Metadata are required to fulfill a specific purpose or to achieve a specific result“(informal definition, Wikipedia)

• „Metadata are structures, encoded data that describe the characteristics of information bearing entities for the purpose of identification, retrieval, evaluation and administration of the described entities.“(W. R. Durrell: Data Administration: A practical Guide to Data Administration. McGraw – Hill, 1985)

• „Metadata is machine understandable information about web resources or other things“ (Tim Berners-Lee: Axioms of Web Architecture: Metadata, 1997)

URI, Ressource and Metadata

http://www.tour-eiffel.fr/index.htmlURI

Information about the Eiffel Tower

Resource:Eiffel Tower Metadata

Metadata: Content-type: text/htmlData:<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html> <head> <title>Le site officiel de la Tour Eiffel</title> ...</html>

Representation

identifies

represents

describes

Resource:Eiffel Tower

(stands for)

(designates)

Address

Uniform Resource Identifier

■ URI combines□ Address (Locator)

□ Uniform Resource Locator (URL, RFC 1738)□ denotes, where a resource can be found in the Web by stating its

primary access mechanism□ might change during life cycle

□ Identity (Name)

□ Uniform Resource Name (URN, RFC 2141)□ persistent identifier for a Web resource□ remains unchanged during life cycle

22 ■ US-ASCII Encoding■ Percent Encoding for reserved characters, or characters that do not exist in US-ASCII

encoding existieren pct-encoded = "%" HEXDIG HEXDIG

■ Reserved characters with special function reserved = gen-delims / sub-delims gen-delims = ":" / "/" / "?" / "#" / "[" / "]" / "@“ sub-delims = "!" / "$" / "&" / "'" / "(" / ")" / "*" / "+" / "," / ";" / "="

■ Permitted characters unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"

■ Extension to Universal Character Code (Unicode/ISO 10646)□ Internationalized Resource Identifier (IRI, RFC 3987)

URI - Generic Syntax

URI = schema"://"[userinfo"@"]host[:port][path]["?"query]["#"fragment]

■ schema: e.g. http, ftp, mailto,...■ userinfo: e.g. username:password■ host: e.g. Domain-Name, IPv4/IPv6 Address■ port: e.g. :80 for standard http port■ path: e.g. path in file system of WWW server■ query: e.g. parameters to be passed over to applications■ fragment: e.g. determines a specific fragment of a document

24 Media Fragment Identifier■ Multimedia Data cover temporal and spatial dimension■ pinpoint acces to multimedia resources via URI Media Fragment Identifier

(W3C Media Fragments URI 1.0, 25. September 2012, W3C Recommendation)■ Example:

■ WWW Client and WWW Server have to take care for handling media fragments correctly, i.e. consequences for http protocol

http://www.example.com/example.ogg#track=‘audio‘http://www.example.com/example.ogg#track=‘audio‘&t=10s,20shttp://www.example.com/example.ogg#track=‘video‘&xywh=160,120,320,240

■ What if a URI for a resource does not exist?■ Define a URI by yourself:□ avoid overlaps

use your own website □ enables documentation at the same place

( Content Negotiation)■ Separate URI for resource (Designatum) and its documentation (Designator)

via URI references (i.e. via "#" fragments) or Content Negotiation

z.B.: http://hpi.uni-potsdam.de/harald_foaf.rdf#me

URIs im Semantic Web

Sauermann, Cyganiak: Cool URIs for the Semantic Web, W3C Interest Group Note 03 December 2008, http://www.w3.org/TR/cooluris/

To a computer, then, the web is a flat, boring world devoid of meaning. This is a pity, as in fact documents on the web describe real objects and imaginary concepts, and give particular relationships between them. For example, a document might describe a person. The title document to a house describes a house and also the ownership relation with a person. [...]

Tim Berners-Lee: W3 future directions, Plenary at 1st WWW Conference, 1994, Geneva (Switzerland)

■How do I represent:

„Harald Sack has the phone number ++49 (331) 5509-527“

<phonenr> <owner>Harald Sack</owner> <number>++49 (331) 5509-527</number></phonenr>

is there a unique (intuitive) way to model knowledge?

Knowledge Representation... a simple example

Harald Sack

has the phone number

++49 (331) 5509-527

„Harald Sack has the phone number ++49 (331) 5509-527“

Harald Sackhas phone number

++49 (331) 5509-527

„Harald Sack has the phone number ++49 (331) 5509-527“■ Intuitive knowledge representation with directed graphs

Knowledge Representation and Communication

Conceptual Domain ModelObjects and Relations

<xsd:schema xmlns:xsd="http://..."><xsd:annotation> Schema A</xsd:...</xsd:schema> XML Schema

is translated into

Senderuses schema A

Receiveruses schema A

XML-based communicationvia schema A

XML-Parser

Deployment

■Problem: new communication partners will not understand

Senderuses schema A

Receiveruses schema A

XML-based communicationvia schema A

XML-Parser

new communication partneruses Schema B

new communication partner uses Schema C

■Schemata have to be translated

Reengineering ofconceptual model

Matching

XML DocumentTranslation

Generation (XSLT)

XML DocumentTranslation

Schemata A <-> B

<xsd:schema xmlns:xsd="http://..."><xsd:annotation> A-Schema</xsd:...</xsd:schema>

<xsd:schema xmlns:xsd="http://..."><xsd:annotation> B-Schema</xsd:...</xsd:schema>

Schema A Schema B

<xsl:stylesheet version="1.0”xmlns:xsl="http://....Transform"<xsl:template match="/">....</xsl:template></xsl:stylesheet>

■Schemata have to be translated■Problems:□Reengineering is expensive and complicated□Reengineering would not be necessary with a conceptual knowledge

representation languagh□Schema translations (XSLT) are expensive and not necessary

use abstract level above XML

Resource Description Framework (RDF)• simple and extensible

Level 1(Objekte)

XMLXMLSchema

Level 3(abgeschlossene

Welten)

RDFRDFSchema

Level 2(Wissen über

Objekte)

Resource■ can be everything (in principle)...■must be uniquely identified and be referencable■ ...simply via URI

Resource Description Framework

Description■ = Descriptions of resources■ ...via representing their relationships among each other■ ...relationships can be represented as graphs

Framework■ = Combination of web based protocols (URI, HTTP, XML,...)■ based on formal model (semantics)■ defines all allowed relationships among resources

■Originally developed to define metadata for web resources ■ 1995-1997: proprietary Meta Content Framework (Netscape)■ 1997 RDF as general description language for metadata, W3C Draft■ 1998 first RDF W3C recommendation (http://www.w3c.org/RDF)

■Definition of an XML subset (machine readable) with predefined (fixed) semantics (machine understandable)

■ Simple, universal semantic data model■ RDF enables high interoperability

Harald Sack

has phone number

++49 (331) 5509-527

Subject

Property

Object

Harald Sack

has phone number

++49 (331) 5509-527

■ Knowledge in RDF is expressed as a list of statements■ all RDF statements follow the same simple schema

Harald Sack

has phone number

++49 (331) 5509-527

Subject

Property

Object

• Resources:Objects that can be addressed via URI

• Properties:Attributes for the description of resources

• Statements (RDF-Triple):Resource + Property + Object / Value

URI URI URI / Literal

Constituents of the RDF-Graphen• URI:

• to reference resources uniquely

http://hpi-web.de/HaraldSack http://swt1213.blogspot.com/

http://hpi-web.de/Personal#writesBlog

Constituents of the RDF-Graphen• Literals:

• describe data values that do not have a separate existence• strings, interpretation via datatype

http://hpi-web.de/HaraldSack ++49-331-5509-527

http://hpi-web.de/Personal#hasPhoneNumber

Constituents of the RDF-Graphen• Literals:

• typed literals can be expressed via XML Schema datatypes• Namespace for typed literals: http://www.w3.org/2001/XMLSchema#

• Example: “Semantics“^^<http://www.w3.org/2001/XMLSchema#string>

• Language Tags denote the (natural) language of the text:• Example: “Semantik“@de , “Semantics“@en

Constituents of the RDF-Graphen• Blank Nodes:

• Denotes existence of an individual with specific attributes, but without providing an identification or reference

htttp://www.hpi-web.de/personal#person

rfds:typeP

RDF Representations• Node-Edge-Node Triple

http://hpi-web.de/HaraldSack

http://hpi-web.de/Personal#writesBlog

http://swt1213.blogspot.com/

RDF Representations• N3 Notation

•Simple listing of triples• { http://hpi-web.de/HaraldSack, http://hpi-web.de/Personal#writesBlog, http://swt1213.blogspot.com/ }

RDF Representations• Turtle (Terse RDF Tripel Language)• Extension of N3• URIs in angle brackets• Literals in quotation marks• Triple ends with a period• Whitespaces will be ignored

<Subject> <Property> <Object> .<Subject> <Property> “Object“ .

RDF Representations• Turtle (Terse RDF Tripel Language)

<http://hpi-web.de/HaraldSack> <http://hpi-web.de/Personal#writesBlog> <http://swt1213.blogspot.com/>.

<http://hpi-web.de/HaraldSack> <http://hpi-web.de/Personal#hasPhoneNumber> “++49-331-5509-527“.

RDF Representations• Turtle (Terse RDF Tripel Language)

@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .@prefix dc: <http://purl.org/dc/elements/1.1/> .@prefix ex: <http://example.org/stuff/1.0/> .

<http://www.w3.org/TR/rdf-syntax-grammar> dc:title "RDF/XML Syntax Specification (Revised)"@en ; ex:editor [ ex:fullname "Dave Beckett"^^xsd:string ; ex:homePage <http://purl.org/net/dajobe/> ] .

RDF Representations• RDF XML-Serialization

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:hasPhoneNr>++49-331-5509-527</pers:hasPhoneNumber> </rdf:Description>

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:writesBlog> <rdf:Description rdf:about=“http://swt1213.blogspot.com/“></rdf:Description> </pers:writesBlog> </rdf:Description></rdf:RDF>

hasPhoneNumber

http://swt1213.blogspot.com/writesBlog

Resource

Literal

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:hasPhoneNumber>++49-331-5509-527</pers:hasPhoneNumber> <rdf:Description>

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:writesBlog rdf:resource=“http://swt1213.blogspot.com/“ /> </rdf:Description></rdf:RDF>

Resource

++49-331-5509-527

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:hasPhoneNumber>++49-331-5509-527</pers:hasPhoneNumber> <rdf:Description>

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:writesBlog rdf:resource=“http://swt1213.blogspot.com/“ /> </rdf:Description></rdf:RDF>

Resource

Literal

Resource

++49-331-5509-527hasPhoneNumber

Resource

Literal

Resource

++49-331-5509-527

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“ pers:hasPhoneNumber=“++49-331-5509-527“> <pers:writesBlog rdf:resource=“http://swt1213.blogspot.com/“/> </rdf:Description></rdf:RDF>

hasPhoneNumber

http://hpi-web.de/Dozenten#HaraldSack

Resource

Literal

Resource

++49-331-5509-527

<xml version=“1.0“ encoding=“utf-8“><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#“ xmlns:pers=“http://hpi-web.de/Personal#“

xml:base=“http://hpi-web.de/Dozenten“>

<rdf:Description rdf:about=“#HaraldSack“ pers:hasPhoneNumber=“++49-331-5509-527“> <pers:writesBlog rdf:resource=“http://swt1213.blogspot.com/“/> </rdf:Description></rdf:RDF>

hasPhoneNumber

Resource

Literal

Resource

++49-331-5509-527

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix pers: <http://hpi-web.de/Personal#> .@base <http://hpi-web.de/Dozenten> .

:HaraldSack pers:hasphoneNumber “++49-331-5509-527“ .:HaraldSack pers:writesBlog <http://swt1213.blogspot.com/> .

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix pers: <http://hpi-web.de/Personal#> .@base <http://hpi-web.de/Dozenten> .

:HaraldSack pers:hasPhoneNumber “++49-331-5509-527“ ; pers:writesBlog <http://swt1213.blogspot.com/> .

Short Cut

hasPhoneNumber

Resource

Literal

Resource

++49-331-5509-527

<xml version=“1.0“ encoding=“utf-8“><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#“ xmlns:pers=“http://hpi-web.de/Personal#“ xml:base=“http://hpi-web.de/Dozenten“

<rdf:Description rdf:ID=“HaraldSack“ pers:hasPhoneNumber=“++49-331-5509-527“> <pers:writesBlog rdf:resource=“http://swt1213.blogspot.com/“/> </rdf:Description></rdf:RDF> Datei http://hpi-web.de/Dozenten.rdf

hasPhoneNumber

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix pers: <http://hpi-web.de/Personal#> .

:HaraldSack pers:hasPhoneNumber “++49-31-5509-527“ ; pers:writesBlog <http://swt1213.blogspot.com/> .

Resource

Literal

Resource

++49-331-5509-527

Datei http://hpi-web.de/Dozenten.rdf

hasPhoneNumber

http://hpi-web.de/ws1213#swt

http://hpi-web.de/Lecture#Name

http://hpi-web.de/Lecture#SWS

<rdf:Description rdf:about=“http://hpi-web.de/ws1213#swt“> <lv:Name rdf:datatype=“http://www.w3c.org/2001/XMLSchema#string“> Semantic Web Technologies </lv:Name> <lv:SWS rdf:datatype= “http://www.w3c.org/2001/XMLSchema#integer“> 4 </lv:SWS> </rdf:Description></rdf:RDF>

Semantic Web Technologieshttp://hpi-web.de/Lecture#Name

http://hpi-web.de/Lecture#SWS4

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix lv: <http://hpi-web.de/Lecture#> .

<http://hpi.web.de/ws1213#swt> lv:Name “Semantic Web Technologies“^^<http://www.w3c.org/2001/XMLSchema#string> ; lv:SWS “4“^^<http://www.w3c.org/2001/XMLSchema#integer> .

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix lv: <http://hpi-web.de/Lecture#> .

<http://hpi.web.de/ws1213#swt> lv:Name “Semantic Web Technologies“; lv:SWS 4 . Abgekürzte

Schreibweise

Multi Valued Relations and Blank Nodes• Example: • A lecture takes place twice a week in two different rooms• How to model this in RDF?

Problem: not unique

http://hpi-web.de/Lecture#hasName

http://hpi-web.de/Lecture#hasRoom

http://hpi-web.de/Lecture#hasDate

Die 13.30-15.00

http://hpi-web.de/Lecture#hasRoom

http://hpi-web.de/Lecture#hasDate

H-1.52

Mi 13.30-15.00

Multi Valued Relations and Blank Nodes• Example: • A lecture takes place twice a week in two different rooms• How to model this in RDF?

hpi-lv:hasRoom

Semantic Web Technologieshpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

H-1.52

Mi 13.30-15.00

hpi-lv:hasRoom

hpi-lv:hasDate

hpi-lv:takesPlace

Blank Nodes• Blank Nodes (Bnodes) can be introduced to represend multi valued

relationships• Blank Nodes can be introduced for resources that don‘t need a name

(auxiliary nodes)

hpi-lv:hasRoom

hpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

hpi-lv:takesPlace

Anonymous Blank Nodes

hpi-lv:hasRoom

hpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

hpi-lv:takesPlace

<rdf:Description rdf:about=“http://hpi-web.de/ws1213#swt“> <hpi-lv:takesPlace rdf:parseType=“Resource“/> <hpi-lv:hasDate>Die, 13.30-15.00</hpi-lv:hasDate> <hpi-lv:hasRoom>HS3</hpi-lv:hasRoom> </hpi-lv:takesPlace> </rdf:Description>

Anonymous Blank Nodes

hpi-lv:hasRoom

hpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

hpi-lv:takesPlace

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix hpi-lv: <http://hpi-web.de/Lecture#> .

<http://hpi-web.de/ws1213#swt> hpi-lv:takesPlace [ hpi-lv:hasDate “Die 13.30-15.00“; hpi-lv:hasRoom “HS3“ ] .

Dereferencable Blank Nodes

hpi-lv:hasRoom

hpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

hpi-lv:takesPlace

<rdf:Description rdf:about=“http://hpi-web.de/ws1213#swt“> <hpi-lv:takesPlace rdf:nodeID=“ID1“/> <rdf:Description>

<rdf:Description rdf:nodeID=“ID1“> <hpi-lv:hasDate>Die 13.30-15.00</hpi-lv:hasDate> <hi-lv:hasRoom>HS3<hpi-lv:hasRoom> </rdf:Description></rdf:RDF>

Dereferencable Blank Nodes

hpi-lv:hasRoom

hpi-lv:hasName

Die 13.30-15.00

hpi-lv:hasDate

hpi-lv:takesPlace

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix hpi-lv: <http://hpi-web.de/Lecture#> .

<http://hpi-web.de/ws1213#swt> hpi-lv:takesPlace _:ID1 .

_:ID1 hpi-lv:hasDate “Die 13.30-15.00“; hpi-lv:hasRoom “HS3“ .

Lists• General Data structure to enumerate any resoures or literals• Only shortcuts, no additional semantic expressivity

• Distinguish between• Container

open list, i.e. extension (new entries) possible• Collections

closed list, i.e. no extension possible

RDF Container

rdf:type

rdf:Seq

hpi-lv:hasParticipants

http://hpi-web.de/SchmidtJoseph

http://hpi-web.de/SchulzeEgon

http://hpi-web.de/MuellerFranz

http://hpi-web.de/BurgerAntonrdf:_1

rdf:_2

rdf:_3

rdf:_4

@prefix hpi-lv: <http://hpi-web.de/Lecture#> .@prefix rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

RDF Container

<rdf:Description rdf:about=“http://hpi-web.de/ws1213#swt“> <lv:hasParticipants> <rdf:Seq> <rdf:li rdf:resource=“http://hpi-web.de/BurgerAnton“ /> <rdf:li rdf:resource=“http://hpi-web.de/MuellerFranz“ /> <rdf:li rdf:resource=“http://hpi-web.de/SchmidtJoseph“ /> <rdf:li rdf:resource=“http://hpi-web.de/SchulzeEgon“ /> </rdf:Seq> </lv:hasParticipants> </rdf:Description>

RDF-Container• the root node of the container is

assigned a container-typ via rdf:type• rdf:Bag

unordered set of elements,there is no given order of elements

• rdf:Seqordered set of elements,

• rdf:Altdefines alternatives of elements only one element of the given alternatives is relevant for the application

RDF Container

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@prefix lv: <http://hpi-web.de/Lecture#> .@base <http://hpi-web.de/>

:swt lv:hasParticipants [ a rdf:Seq; rdf:_1 <BurgerAnton>; rdf:_2 <MuellerFranz>; rdf:_3 <SchmidtJoseph>; rdf:_4 <SchulzeEgon> . ] .

RDF-Collection

rdf:nil

lv:hasParticipants rdf:first

rdf:rest

http://hpi-web.de/SchmidtJoseph

http://hpi-web.de/SchulzeEgon

http://hpi-web.de/MuellerFranz

http://hpi-web.de/BurgerAnton

List is splitted recursively in Head (first) and Tail (rest).

rdf:rest

rdf:first

RDF-Collection

<rdf:Description rdf:about=“http://hpi-web.de/ws1213#swt“> <lv:hasParticipant rdf:parseType=“Collection“> <rdf:Description rdf:about=“http://hpi-web.de/BurgerAnton“ /> <rdf:Description rdf:about=“http://hpi-web.de/MuellerFranz“ /> <rdf:Description rdf:about=“http://hpi-web.de/SchmidtJoseph“ /> <rdf:Description rdf:rabout=“http://hpi-web.de/SchulzeEgon“ /> </lv:hasParticipant> </rdf:Description>

RDF-Collection

:swt lv:hasParticipant [ rdf:first <BurgerAnton>; rdf:rest [ rdf:first <MuellerFranz>; rdf:rest [ rdf:first <SchmidtJoseph>; rdf:rest [ rdf:first <SchulzeEgon>; rdf:rest rdf:nil .] ] ] ] .

RDF-Collection

:swt lv:hasParticipant ( <BurgerAnton> <MuellerFranz> <SchmidtJoseph> <SchulzeEgon>) .

What can we model with RDF?

„My dear Watson,...I suppose that the Gardenerhas killed the Butler!“

RDF-Reification• RDF permits interleaving of statements,

i.e. to make statements about statements• Example:

„My dear Watson,...I suppose that the Gardenerhas killed the Butler!“

RDF-Reification• RDF permits interleaving of statements, i.e. to make statements about

statements• Example:• Sherlock Holmes supposes that the Gardener has killed the Butler

•Part 1: The Gardener has killed the Butler

•Part 2: Sherlock Holmes supposes

exv:Gardener exv:hasKilled exv:Butler .

exv:SherlockHolmes exv:supposes ???? .

RDF-Reification• rdf:Statement

defines an RDF Statement, consisting of Subject, Predicate and Object• rdf:subject - the described resource

• rdf:predicate - the original property

• rdf:object - the value of the property

<rdf:Description rdf:about=“http://example.org/StatementOnGaertner“> <rdf:subject rdf:resource=“http://example.org/Gardener“ /> <rdf:predicate rdf:resource=“http://example.org/Crime#hasKilled“ /> <rdf:object rdf:resource=“http://example.org/Butler“ /> <rdf:type rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /></rdf:Description>

RDF-Reification

<rdf:Description rdf:about=“http://example.org/StatementOnGardener“> <rdf:subject rdf:resource=“http://example.org/Gardener“ /> <rdf:predicate rdf:resource=“http://example.org/Crime#hasKilled“ /> <rdf:object rdf:resource=“http://example.org/Butler“ /> <rdf:type rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /></rdf:Description>

<rdf:Description rdf:about=“http://example.org/SherlockHolmes“> <exv:supposes rdf:resource=“http://example.org/StatementOnGaertner“ /> </rdf:Description>

SherlockHolmes

exv:supposes

StatementOnGardener

Gardener

exv:hasKilled

Butler

rdf:subject

rdf:predicate

rdf:object

RDF-Reification

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .@exv <http://example.org/Crime#>

<SherlockHolmes> exv:supposes <StatementOnGardener> .<StatementOnGardener> a rdf:Statement ; rdf:subject <Gardener> ; rdf:predicate exv:hasKilled ; rdf:object <Butler> .

SherlockHolmes

exv:supposes

StatementOnGardener

Gardener

exv:hasKilled

Butler

rdf:subject

rdf:predicate

rdf:object

RDF-Reification• Is Reification really necessary?• Modeling data provenance • Formalizing statements about Reliability (Trust) • Definition of Metadata about Statements (Assertions, Statements)

• for (general) knowledge representation (Ontologie Construction):• Transformation of Relations into Classes

RDF and Data Integration

• Simple Example: Bibliography Database

ID Author Title Publisher Year

ISBN 0-00-651409-X HS-123 WWW S-001 2004

ID Name Homepage

HS-123 Harald Sack http://hpi-web.de/HaraldSack.html

ID Publisher Location

S-001 Springer Heidelberg

ISBN 0-00-651409-X

a:title

a:year

Springer

Heidelberg

a:publishername

a:publisherlocation

a:publisher

Harald Sack

http://hpi-web.de/HaraldSack.html

a:authorname

a:authorhomepage

a:author

• Database export into a set of relations

ISBN 0-00-651409-X

u:author

Harald Sack

u:name

http://.../paper

u:cites

Very important paper

u:title

ISBN 0-00-651409-X

a:title

a:year

Springer

Heidelberg

a:publishername

a:publisherlocation

a:publisher

Harald Sack

a:authorname

a:authorhomepage

a:author

ISBN 0-00-651409-X

Springer

Heidelberg

Harald Sack

ISBN 0-00-651409-X

u:author

Harald Sack

u:name

http://.../paper

u:cites

u:title

a:title

a:year

a:publishername

a:publisherlocation

a:publisher

a:authorname

a:authorhomepage

a:author

Springer

Heidelberg

Harald Sack

u:author

Harald Sack

u:name

http://.../paper

u:cites

ISBN 0-00-651409-X

u:title

a:title

a:year

a:publishername

a:publisherlocationa:publisher

a:authorname

a:authorhomepage

a:author

RDF - a Resume

RDF Model -- Summary• An RDF Model is a set of RDF statements• Statement := (subject, property, object)• Subject is a resource• Property is a resource• Object is ether a resource or a literal

SO ... WE NEED A WAY TO DEFINE RDF SCHEMATA FORCLASSES AND RELATIONS ?!

Next lecture

Bibliography

• Ch. Meinel, H. Sack: WWW - Kommunikation, Internetworking, Webtechnologien, Springer, 2004.

• D. R. Hofstadter: Gödel, Escher, Bach - ein endlos geflochtenes Band, Dtv, 1992.

2. Semantic Web Basic Architecture2.1 Uniform Resource Identifier2.2 XML und XMLSchema2.3 Resource Description Framework

Bibliography

• P. Hitzler, S. Roschke, Y. Sure: Semantic Web Grundlagen, Springer, 2007.

• P. Hitzler, M. Krötzsch, S. Rudolph:Foundations of Semantic Web Technologies,CRC Press, 2009.

Lecture Semantic Web Technologies, Dr. Harald Sack, Hasso-Plattner-Institut, Universität Potsdam

□Bloghttp://semweb2013.blogspot.com/

□Webseitehttp://www.hpi.uni-potsdam.de/studium/lehrangebot/itse/veranstaltung/semantic_web_technologien-3.html

□bibsonomy - Bookmarkshttp://www.bibsonomy.org/user/lysander07/swt1213_02

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