RDF and OWL

RDF & OWL A simple overview of the b uilding blocks of the Semantic Web Presented by Rachel Lovinger Semantic Web Affinity Group December 2007

RDF = Resource Description Framework

Purpose: To provide a structure (aka framework) for describing identified things (aka resources)
RDF

Identified ?
In order to make meaningful statements in RDF, the thing you’re talking about has to be identified in some unique way.
http://www.foaf.com/Person#RachelLovinger
http://www.allmovie.com/Actor#WillSmith
URIs (uniform resource identifiers) look like URLs, but they may not represent an actual web page.
RDF

Composed of three basic elements
Resources – the things being described
Properties – the relationships between things
Classes – the buckets used to group the things
RDF

The elements are combined to make simple statements in the form of Triples
<Subject> <Predicate> <Object>
Men In Black stars Will Smith
<MenInBlack> <hasStar> <WillSmith>
RDF

Information Expressed in Triples
<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> "Dave Beckett" .
<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:creator> "Art Barstow" .
<http://www.w3.org/2001/sw/RDFCore/ntriples/> <dc:publisher> <http://www.w3.org/> .
Can also be expressed as XML
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/">
<rdf:Description rdf:about="http://www.w3.org/2001/sw/RDFCore/ntriples/"> <dc:creator>Art Barstow</dc:creator>
<dc:creator>Dave Beckett</dc:creator>
<dc:publisher rdf:resource="http://www.w3.org/"/>
</rdf:Description>
</rdf:RDF>
RDF

RDF Properties
type
subClassOf
subPropertyOf
range
domain
label
comment
RDF

type – a resource belongs to a certain class
<WillSmith> <type> <Actor>
This defines which properties will be relevant to Will Smith.
RDF

subClassOf – a class belongs to a parent class
<Actor> <subClassOf> <Person>
This means that all members of the actor class are also members of the Person class. All properties are inherited, and new properties specific to Actor can be added.
<WillSmith> <type> <Actor>
implies <WillSmith> <type> <Person>
RDF

subPropertyOf – a property has a parent property
<hasStar> <subPropertyOf> <hasActor>
This means that, if you make a statement using the hasStar property, a more general statement using the hasActor property is also true.
implies <MenInBlack> <hasActor> <WillSmith>
RDF

range & domain – the types of resources that use a property
<hasStar> <range> <Actor>
<hasStar> <domain> <Movie>
This means that, if you make a statement using the hasStar property, the system will assume that the subject is a Movie and the object is an Actor.
<WillSmith> <hasStar> <MenInBlack>
is an untrue statement, but not invalid
RDF

label – a human-readable name for a resource
<http://www.allmovie.com/Actor#WillSmith> <label> <Will Smith>
RDF

comment – a human-readable description
<https://aarfwiki.main.corp/wiki/index.php/File:RDF_OWL.pdf> <comment> <A presentation that Rachel gave at the December 2007 Semantic Web Affinity Group Meeting>
RDF

RDF Blackberry Fruit typeOf BerryPie EdibleThing typeOf subClassOf ingredientOf Blackberry

Why is RDF uniquely suited to expressing data and data relationships?
More flexible – data relationships can be explored from all angles
More efficient – large scale, data can be read more quickly
not linear like a traditional database
not hierarchical like XML
RDF

Namespaces

A method for qualifying names used in an XML document. Can be used to indicate usage of a standard, or to specify a unique version of the term.
dc:creator
rdf:type
foaf:Person
foaf:knows
aarf:Employee
Namespaces

OWL = Web Ontology Language

Purpose: To develop ontologies that are compatible with the World Wide Web.
OWL

Ontologies ?
Definition and classification of concepts and entities, and the relationships between them.
OWL

Based on the basic elements of RDF; adds more vocabulary for describing properties and classes.
Relationships between classes (ex: disjointWith)
Equality (ex: sameAs)
Richer properties (ex: symmetrical)
Class property restrictions (ex: allValuesFrom)
OWL

Relationships between Classes
disjointWith – resources belonging to one class cannot belong to the other
<Person> <disjointWith> <Country>
complementOf – the members of one class are all the resources that do not belong to the other
<InanimateThings> <complementOf> <LivingThings>
OWL

Equality
sameAs – indicates that two resources actually refer to the same real-world thing or concept
<wills> <sameAs> <wismith>
equivalentClass – indicates that two classes have the same set of members
<CoopBoardMembers> <equivalentClass> <CoopResidents>
OWL

Richer Properties
Symmetric – a relationship between A and B is also true between B and A
<WillSmith> <marriedTo> <JadaPinkettSmith>
implies <JadaPinkettSmith> <marriedTo> <WillSmith>
Transitive – a relationship between A and B and between B and C is also true between A and C
<piston> <isPartOf> <engine>
<engine> <isPartOf> <automobile>
implies <piston> <isPartOf> <automobile>
OWL

Richer Properties continued
inverseOf – a relationship of type X between A and B implies a relationship of type Y between B and A
<starsIn> <inverseOf> <hasStar>
implies <WillSmith> <starsIn> <MenInBlack>
OWL

Class Property Restrictions – define the members of a class based on their properties
allValuesFrom – resources with properties that only have values that meet this criteria
Example: Property: hasParents, allValuesFrom: Human
Resources that meet this criteria can be defined as also being members of the Human class
someValuesFrom – resources with properties that have at least one value that meets criteria
Example: Property: hasGraduated, someValuesFrom: College
Resources that meet this criteria can be defined as being members of the CollegeGraduates class
OWL

This seems complicated. Why do it?
These capabilities allows systems to express and make sense of first order logic.
All men are mortal
Socrates is a man
Therefore, Socrates is mortal
OWL

Inferences
Create new triples based on existing triples
Deduce new facts based on the stated facts
<piston> <isPartOf> <engine>
<engine> <isPartOf> <automobile>
implies <piston> <isPartOf> <automobile>
OWL

Three Flavors of OWL
OWL Lite – uses a subset of the capabilities
OWL DL – uses all the capabilities, but some are used in restricted ways
OWL Full – unrestricted use of capabilities; no guarantee that all resulting statements are valid
OWL

SKOS = Simple Knowledge Organization System

Also based on RDF
Designed specifically to express information that’s more hierarchical – broader terms, narrower terms, preferred terms and other thesaurus-like relationships
Extendable into OWL, if needed
SKOS

Need more?

SchemaWeb: http://www.schemaweb.info/default.aspx
RDF Primer: http://www.w3.org/TR/REC-rdf-syntax/
OWL / Semantic Web: http://www.w3.org/2004/OWL/
SKOS: http://www.w3.org/2004/02/skos/
Dublin Core: http://dublincore.org/
Namespaces: http://www.w3.org/TR/REC-xml-names/
URIs: http://www.w3.org/Addressing/
Resources

http://www.scienceforseo.com	201
http://www.slideshare.net	74
https://twimg0-a.akamaihd.net	32
http://e-reality-database.blogspot.com	7
http://www.linkedin.com	3
http://us-w1.rockmelt.com	2
http://translate.googleusercontent.com	1

RDF and OWL

by Rachel Lovinger

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RDF and OWL Presentation Transcript