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RDF Resource Description Framework

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Title: RDF Resource Description Framework


1
RDF ResourceDescription Framework
Una piattaforma inferenziale per il Web
Semantico Jena2 Roma, 2006 Web Semantico
  • M. Missikoff F. Taglino
  • LEKS, IASI-CNR

2
Summary
  • Motivations
  • RDF knowledge model
  • RDF(S) modelling notions
  • XML/RDF, an XML syntax for RDF(S)
  • Using RDF for inferring knowledge
  • Extending RDF(S) OWL
  • Conclusions

3
Motivations
  • Semantic Web Information needs to be processed
    by applications, rather than being only displayed
    to people (e.g., like with HTML)
  • Common convention about semantics, syntax, and
    structure required
  • Define a language for representing meta-data,
    with a semantic flavor

4
What is RDF?
  • The Resource Description Framework is a
  • Flexible language for representing knowledge over
    the web
  • It models conceptual knowledge (schemas) and
    factual knowledge (data)
  • Enables the encoding, exchange, and reuse of
    structured knowledge about defined entities
    (identified by URI)
  • Enables data interoperability through the design
    of mechanisms that support common conventions of
    semantics, syntax, and structure.
  • The
  • W3C Recommendation
  • http//www.w3.org/TR/rdf-syntax-grammar/

5
URI - Uniform Resource Identifier
  • Used to identify items on the Web
  • Anyone can create a URI
  • A URI can be associated to anything
  • Network-accessible things, e.g., electronic
    document, image, service,
  • Not network-accessible things, e.g., human
    beings, corporation, book, car,
  • Abstract concepts, e.g., creator, member,
  • Uniform Resource Locator (URL) one form of URI
    e.g., http//www.w3.org

6
RDF (Meta)Model
  • Knowledge is represented as collections of Triples

resource (subject)
property (predicate)
value (object)
  • Resource thing that can be identified on the
    Web
  • Property specific aspect, characteristic,
    attribute, or relation used to describe a
    resource
  • Value - Propertys value resource or literal
  • Connecting triples together we can represent a
    graph

7
RDF abstract (graph) representation
mary
has_sister
john
27
has_age
type
john
Person
subClassOf
Student
Prof
8
Statement (triple)
  • The following sentence
  • http//www.example.org/index.html has creator
    whose_value_is John Smith
  • Can be expressed by an RDF statement having
  • Subject http//www.example.org/index.html
  • Predicate http//purl.org/dc/creator
  • Object John Smith

9
Basic RDF Model - example
  • http//www.example.org/index.html has creator
    whose value is John Smith

http//www.example.org/ index.html
http//purl.org/dc/creator
John Smith
resource (subject)
property (predicate)
value (object)
RDF Statement
Please Note when the object is a Literal it is
represented by a BOX
10
RDF Schema
  • The purpose is to define an XML vocabulary to
  • Denote classes (subclasses) and their
    relationships
  • Define properties and associate them with classes
  • The benefit is that
  • Data are modeled according to schema (as usual in
    DB)
  • inferencing on data, and enhanced searching are
    facilitated
  • http//www.w3.org/TR/rdf-schema/

11
Knowledge model of RDF(S)
RDF(S) Meta-model
property
Class
range
Application specific schema (RDF(S) Model)
has_age
Person
Int
Application specific actual data (RDF Instances)
has_age
23
John
12
RDF(S) modelling notions
  • The following RDF(S) modelling notions are
    presented
  • Schema definition useful for defining new
    vocabularies (i.e., names of classes, of
    attributes, )
  • Utility additional notions useful to enrich the
    entity definiton
  • Label and Comment
  • Complex Structures, e.g., Container
  • Synonyms
  • Note we will present a simplified version of
    RDF(S). In particular, reification will be
    omitted

13
Schema definition (RDFS vocabulary)
  • rdfsClass
  • Set of resources
  • rdfssubClassOf
  • For defining specialisation among Classes
  • rdfsdomain and rdfsrange
  • Constraints on properties definition
  • rdfssubProperty
  • For defining specialisation among Properties
  • rdfProperty
  • Borrowed from RDF (ground), but used at schema
    level

14
rdfsClass
  • Class is a resource denoting a set of resources
    (instances)
  • Examples
  • Person
  • River

Person
rdfsClass
River
ltrdfsClass rdfIDRiver/gt ltrdfsClass
rdfIDPerson/gt
15
rdfssubClassOf Example
NaturallyOccurringWaterSource
rdfssubClassOf
BodyOfWater
Stream
Lake
Ocean
Sea
Brook
River
Tributary
  • ltrdfsClass rdfIDNaturallyOccurringWaterSource
    /gt
  • ltrdfsClass rdfIDBodyOfWater/gt
  • ltrdfssubClassOf rdfresourceNaturallyOccurr
    ingWaterSource/gt
  • lt/rdfsClassgt
  • ltrdfsClass rdfIDStreamgt
  • ltrdfssubClassOf rdfresourceNaturallyOccurr
    ingWaterSource/gt
  • lt/rdfsClassgt
  • ltrdfsClass rdfIDRivergt
  • ltrdfssubClassOf rdfresourceStream/gt
  • lt/rdfsClassgt

16
rdfssubClassOf Properties
  • Allows specialisation hierarchy among Classes to
    be defined
  • Multiple subClassOf properties may be specified
  • Transitive (i.e., any River is a
    NaturallyOccurringWaterSource too)

17
Definition of a Property at intensional level
rdfsdomain and rdfsrange
  • Used to define properties at intentional level
  • rdfsdomain, restricts the set of resources that
    may have a given property
  • rdfsrange, restricts the set of valid values for
    a property.
  • A property may have multiple domain, and more
    than one range

18
Example of definition of a Property at
intensional level (1)
A River has a name expressed as a Literal
rdfsClass
River
rdfsdomain
rdfProperty
hasName
Class representing literals (strings)
rdfsLiteral
rdfsrange
  • ltrdfsClass rdfIDRiver/gt
  • ltrdfProperty rdfIDhasNamegt
  • ltrdfsdomain rdfresourceRiver/gt
  • ltrdfsrange rdfresourcehttp//www.w3.org/200
    0/01/rdfschemaLiteral/gt
  • lt/rdfPropertygt

19
Example of definition of a Property at
intensional level (2)
rdfsClass
River
rdfsdomain
rdfProperty
emptiesInto
rdfsClass
BodyOfWater
rdfsrange
  • ltrdfProperty rdfIDemptiesIntogt
  • ltrdfsdomain rdfresourceRiver/gt
  • ltrdfsrange rdfresourceBodyOfWater/gt
  • lt/rdfPropertygt

20
rdfssubPropertyOf
  • Allows specialisation hierararchy among
    properties to be defined
  • Multiple subPropertyOf properties for the same
    property can be specified

21
Example of a subProperty definition
The hasMother property is a sub property of the
hasParent property
rdfsdomain
rdfProperty
rdfsClass
Person
hasParent
rdfssubPropertyOf
rdfsrange
hasMother
rdfProperty
  • ltrdfProperty rdfIDhasParentgt
  • ltrdfsdomain rdfresourcePerson/gt
  • ltrdfsrange rdfresourcePerson/gt
  • lt/rdfProperty gt
  • ltrdfProperty rdfIDhasMothergt
  • ltrdfssubPropertyOf rdfresourcehasParent/gt
  • lt/rdfPropertygt

22
Class instance definitionrdftype
  • Instances are defined through the rdftype
    property

The Yangtze is an instance of the River Class
rdftype
Yangtze
River
ltrdfDescription rdfIDYangtzegt ltrdftype
rdfresourceRiver/gt lt/rdfDescriptiongt
23
Utility notions
  • rdfslabel and rdfscomment
  • For describing resources with human readable text
  • rdfsContainer
  • Collections of resources
  • rdfsseeAlso and rdfsisDefinedBy
  • For referring to alternative descriptions of
    resources

24
rdfslabel and rdfscomment
  • Describe a resource with human readable text in
    addition to pure RDF properties
  • rdfslabel, to assign a human readable name to a
    resource
  • rdfscomment, to give a longer natural language
    description to a resource

Yangtze
rdfslabel
http//www.china.org/geography/ rivers/Yangtze
The biggest Chinese river
rdfscomment
ltrdfDescription rdfIDhttp//www.china.org/geog
raphy/rivers/Yangtzegt ltrdfslabelgtYangtzelt/rdf
slabelgt ltrdfscommentgtThe biggest Chinese
riverlt/rdfscommentgt lt/rdfPropertygt
25
Summary of RDF(S) modeling constructs
  • rdfsClass and rdftype
  • rdfssubClassOf
  • rdfsdomain and rdfsrange
  • rdfssubProperty and rdfproperty
  • rdfslabel and rdfscomment
  • rdfsContainer
  • rdfsseeAlso and rdfsisDefinedBy
  • rdfResource (the generic entity)
  • rdfID (when the entity is first introduced)
  • rdfabout (when the entity is referred to)
  • rdfDescription

26
How RDF can be implemented
  • Diagrammatic representation is an Abstract Syntax
  • Several Concrete Sintaxes usually RDF/XML syntax
  • However, other notations possible
  • e.g., Notation3 (N3)
  • ltpatgt ltlovesgt ltjoegt
  • lthttp//xyz.org/agt lthttp//xyz.org/bgt
    lthttp//xyz.org/cgt
  • lthttp//xyz.org/Seangt lthttp//xyz.org/namegt
    Sean
  • RDF/XML Abreviated syntax

Note the symbol is a separator between the
Prefix and the resource ID
27
Using RDF(S) for Ontologies and Inferencing
28
An extract of an RDF ontology
  • lt?xml version1.0/gt
  • ltrdfRDF xmlnsrdfhttp//www.w3.org/1999/02/22-r
    df-syntax-ns
  • xmlnsrdfshttp//www.w3.org/2000/
    01/rdf-schema
  • xmlbasehttp//www.geodesy.org/wa
    ter/naturally-occurringgt
  • ltrdfsClass rdfIDNaturallyOccurringWaterSource
    /gt
  • ltrdfsClass rdfIDBodyOfWater/gt
  • ltrdfssubClassOf rdfresourceNaturallyOccur
    ringWaterSource/gt
  • lt/rdfsClassgt
  • ltrdfsClass rdfIDStreamgt
  • ltrdfssubClassOf rdfresourceNaturallyOccur
    ringWaterSource/gt
  • lt/rdfsClassgt
  • ltrdfsClass rdfIDRivergt
  • ltrdfssubClassOf rdfresourceStream/gt
  • lt/rdfsClassgt
  • ltrdfProperty rdfIDemptiesIntogt
  • ltrdfsdomain rdfresourceRiver/gt
  • ltrdfsrange rdfresourceBodyOfWater/gt
  • lt/rdfPropertygt
  • ltrdfProperty rdfIDlengthgt

29
What inferences can be made?
NaturallyOccurringWaterSource
rdfssubClassOf
Inference Engine
BodyOfWater
Stream
Brook
River
Tributary
Lake
Ocean
Sea
- length Literal - emptiesInto BodyOfWater
ltRiver rdfIDhttp//www.china.org/geography/rive
rs/Yangtze xmlnsrdfhttp//www.w3.org/1999/02
/22-rdf-syntax-ns xmlnshttp//www.geodesy.o
rg/rivergt ltlenghtgt6300 kilometerslt/lenghtgt ltem
ptiesInto rdfresourcehttp//www.china.org/EastC
hinaSea/gt lt/Rivergt
Inferences - Yangtze is a Stream - Yangtze is
a NaturallyOccurringWaterSource -
http//www.china.org/EastChinaSea is a BodyOfWater
30
How does a taxonomy facilitate searching?
NaturallyOccurringWaterSource
rdfssubClassOf
BodyOfWater
Stream
Brook
River
Tributary
Lake
Ocean
Sea
Inference Engine
- length Literal - emptiesInto BodyOfWater
Show me all the documents that contain info
about streams
ltRiver rdfIDhttp//www.china.org/geography/rive
rs/Yangtze xmlnsrdfhttp//www.w3.org/1999/02
/22-rdf-syntax-ns xmlnshttp//www.geodesy.o
rg/rivergt ltlenghtgt6300 kilometerslt/lenghtgt ltem
ptiesInto rdfresourcehttp//www.china.org/EastC
hinaSea/gt lt/Rivergt
Results - Yangtze is a Stream, so this document
is relevant to the query
31
Desire more expressiveness
  • Two classes, same concept
  • Equivalent classes Airplane and Plane
  • Cardinality constraints
  • Ocean has one maxDepth

OWL
RDF Schema Building Block to more expressive
Ontology Languages like OWL
RDF(S)
32
OWL (Ontology Web Language)
  • Provides three increasingly expressive languages
  • OWL Full maximum expressiveness with no
    computational guarantees
  • OWL DL, expressiveness of Description Logics
    without losing computational completeness
  • OWL Lite, simple constraint features. E.g.,
    cardinality constraints

OWL Full
OWL DL
OWL Lite
33
Rules
  • Allows for derivations, by introducing a
    special binary predicate
  • logimplies gt
  • Subject and Object are RDF triples, called
    formulae
  • Derivation (n3 syntax)
  • X parent Y brother Z gt Z uncle Y

34
Conclusions
  • RDF has potential to make web contents machine
    readable
  • RDF describes resources and anything can be seen
    as a Resources
  • RDF(S) comprises vocabulary for describing also
    the intentional level
  • Several serializations (i.e., RDF/XML, N3)
  • Suitable for applying inference
  • Limited features (i.e., no cardinality
    constraints)
  • OWL for a more expressiveness

35
Sources
  • http//www.w3.org/TR/rdf-primer/
  • http//www.w3.org/TR/rdf-syntax-grammar/
  • http//www.w3.org/TR/rdf-schema/
  • P.A. Champin, RDF Tutorial - http//www710.univ-ly
    on1.fr/champin/rdf-tutorial/rdf-tutorial.pdf
  • A. Wilk, RDF(S) - www.ida.liu.se/labs/iislab/cours
    es/LW/slides/RDFS.pdf

36
Qualche esercizio rapido
  • Rappresentare in RDF alcune frasi di linguaggio
    naturale
  • Ugo ama Anna
  • Il treno parte alle 1040
  • Il treno è partito in ritardo
  • Le auto vecchie inquinano
  • Il corso di Knowledge Extraction è interessante
  • La prima domenica del mese cè il mercatino in
    Piazza Dante

37
Passaggio a RDF/Diagramma
  • Ugo ama Anna

Persona
RdfssubClassOf
Studente
rdftype
Exama
ExUgo
ExAnna
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