OpenHPI 2.2 - How to Represent Facts - RDF

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Dr. Harald Sack

Hasso Plattner Institute for IT Systems Engineering

University of Potsdam

Spring 2013

Semantic Web Technologies

Lecture 2: Semantic Web - Basic Architecture I02: How to Represent Facts? - RDF(1)

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

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Lecture 2: Semantic Web - Basic Architecture I

Open HPI - Course: Semantic Web Technologies


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02 How to Represent Facts? - RDF (1)Open HPI - Course: Semantic Web Technologies - Lecture 2: Semantic Web Basic Architecture I

Introduction


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


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)


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


■How do I represent:

„Harald Sack has the phone number ++49 (331) 5509-927“

Knowledge Representation... a simple example




<phonenr> <owner>Harald Sack</owner> <number>++49 (331) 5509-927</number></phonenr>







<person name=“Harald Sack“ phone=“49 (331) 5509-927“ />

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



Harald Sack





Harald Sack

has the phone number





Harald Sack

has the phone number

++49 (331) 5509-927








■ Intuitive knowledge representation with directed graphs


Harald Sackhas phone number

++49 (331) 5509-927




■ Intuitive knowledge representation with directed graphs


Level 1(objects)

XMLXMLSchema

Knowledge Representation in the Semantic Web


Level 1(objects)

XMLXMLSchema

RDF &RDFSchema

Level 2(knowledge about

objects)



Level 1(objects)

XMLXMLSchema

Level 3(entire worlds)

OWL & Rules

RDF &RDFSchema

Level 2(knowledge about

objects)



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RDF


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Resource■ can be everything (in principle)...

■must be uniquely identified and be referencable

■ ...simply via URI

Resource Description Framework


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Description■ = Descriptions of resources

■ ...via representing properties and relationships among resources

■ ...relationships can be represented as graphs


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Framework■ = Combination of web based protocols (URI, HTTP, XML,...)

■ based on formal model (semantics)

■ defines all allowed relationships among resources


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Harald Sack

has phone number

++49 (331) 5509-927

Subject

Property

Object


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Harald Sack

has phone number

++49 (331) 5509-927

■ Knowledge in RDF is expressed as a list of statements

■ all RDF statements follow the same simple schema


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Harald Sack

has phone number

++49 (331) 5509-927

Subject

Property

Object


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• 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-Graph• URI:

• to reference resources uniquely


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http://hpi-web.de/HaraldSack http://semweb2013.blogspot.com/

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

S

P

O

http://swt1213.blogspot.co


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


Constituents of the RDF-Graphen• Literals:

• describe data values that do not have a separate existence

• strings, interpretation via datatype


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http://hpi-web.de/HaraldSack ++49-331-5509-927

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

S

P

O



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


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http://www.w3c.org/2001/xml-schema#

http://www.w3c.org/2001/xml-schema#

http://www.w3.org/2001/XML

http://www.w3.org/2001/XML

Constituents of the RDF-Graphen• Blank Nodes:

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


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S

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

rdf:typeP

O

http://www.hpi-web.de/Perspnal#

http://www.hpi-web.de/Perspnal#

RDF Representations• Node-Edge-Node Triple


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http://hpi-web.de/HaraldSack

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

S

P

O

http://semweb2013.blogspot.com/





RDF Representations• N3 Notation

•Simple listing of triples

• { http://hpi-web.de/HaraldSack, http://hpi-web.de/Personal#writesBlog, http://semweb2013.blogspot.com/ }


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

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

http://sewe0910.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


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

RDF Representations• Turtle (Terse RDF Tripel Language)


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<http://hpi-web.de/HaraldSack> <http://hpi-web.de/Personal#writesBlog> <http://semweb2013.blogspot.com/>.

<http://hpi-web.de/HaraldSack> <http://hpi-web.de/Personal#hasPhoneNumber> “++49-331-5509-927“.







RDF Representations• Turtle (Terse RDF Tripel Language)


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@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/> ] .

http://www.w3.org/1999/02/22-rdf-syntax-ns#

http://www.w3.org/1999/02/22-rdf-syntax-ns#

http://purl.org/dc/elements/1.1/

http://purl.org/dc/elements/1.1/

http://example.org/stuff/1.0/

http://example.org/stuff/1.0/

http://www.w3.org/TR/rdf-syntax-grammar

http://www.w3.org/TR/rdf-syntax-grammar

http://purl.org/net/dajobe/

http://purl.org/net/dajobe/

RDF Representations• RDF XML-Serialization


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<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#“>

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:hasPhoneNr>++49-331-5509-927</pers:hasPhoneNumber> </rdf:Description>

<rdf:Description rdf:about=“http://hpi-web.de/HaraldSack“> <pers:writesBlog> <rdf:Description rdf:about=“http://semweb2013.blogspot.com/“></rdf:Description> </pers:writesBlog> </rdf:Description></rdf:RDF>

http://sw0910.blogspot.com

http://sw0910.blogspot.com


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03 How to Represent Facts? - RDF (2)Open HPI - Course: Semantic Web Technologies - Lecture 2: Semantic Web Basic Architecture I

Simple Facts in RDF

OpenHPI 2.2 - How to Represent Facts - RDF

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