RDF and XML tutorial

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RDF and XML tutorial

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Talk Overview

• Semantic Web
• XML
• RDF
• DAML OIL ( Time permitting)

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Problems with current search engines

• Current search engines keywords
• high recall, low precision
• sensitive to vocabulary
• insensitive to implicit content

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Search engines on theSemantic Web

• concept search instead of keyword search
• semantic narrowing/widening of queries
• query-answering over gt1 document
• document transformation operators

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So what is the Semantic Web?

• The Semantic Web Wedding Cake
• Crash course
• XML
• RDF
• RDF Schema
• DAMLOIL (OWL)

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TBL talk at XML 2000
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XML User definable and domain specific markup
HTML
ltH1gtIntroduction to AIlt/H1gt ltULgt ltLIgtTeacher
Frank van Harmelen ltLIgtStudents 1AI,
1I ltLIgtRequirements none lt/ULgt
XML
ltcoursegt lttitlegtIntroduction to
AIlt/titlegt ltteachergtFrank van Harmelenlt/teachergt
ltstudentsgt1AI, 1Ilt/studentsgt ltreqgtnonelt/reqgtlt/c
oursegt
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XML document labelled tree

• node label attr/values contents

ltcourse date...gt lttitlegt...lt/titlegt ltteachergt
...lt/teachergt ltnamegt...lt/namegt lthttpgt...lt/http
gt ltstudentsgt...lt/studentsgtlt/coursegt

• XML Schema grammars for describing legal
  trees and datatypes

• So why not use XML to represent semantics?

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Syntax versus Semantics

• Syntax the structure of your data
• Semantics the meaning of your data
• Two conditions necessary for interoperability
• Adopt a common syntax this enables applications
  to parse the data.
• Adopt a means for understanding the semantics
  this enables applications to use the data.

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XML and Semantics?

• ltPredatorgt
• lt/Predatorgt
• Predator a medium-altitude, long-endurance
  unmanned aerial vehicle system.
• Predator one that victimizes, plunders, or
  destroys, especially for one's own gain.
• Predator an organism that lives by preying on
  other organisms.
• Predator a company which specializes in
  camouflage attire.

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XML limitations for semantic markup

• XML makes no commitment on
• ? Domain-specific ontological vocabulary
• ? Ontological modeling primitives
• Requires pre-arranged agreement on ? ?
• Only feasible for closed collaboration
• agents in a small stable community
• pages on a small stable intranet
• Not suited for sharing Web-resources

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What is RDF ?

• RDF is a data model
• the model is domain-neutral, application-neutral
  and ready for internationalization (i18n)
• the model can be viewed as directed, labeled
  graphs or as an object-oriented model
  (object/attribute/value)
• RDF data model is an abstract, conceptual layer
  independent of XML
• consequently, XML is a transfer syntax for RDF,
  not a component of RDF
• RDF data might never occur in XML form

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RDF model

• RDF statements consist of
• resources ( nodes)which have propertieswhich
  have values ( nodes,strings)

subject predicate object
http//www.w3.org/TR/REC-rdf-syntax/ has the
author Ora Lassila
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RDF Model Example
W3C
dcPublisher
http//www.w3.org/TR/REC-rdf-syntax/
dcCreator
dcDate
Ora Lassila
1999-02-22
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Complex values

• So far, values of properties have been strings
• A graph node (corresponding to a resource) also
  can be the value of a property
• arbitrarily complex tree and graph structures are
  possible
• syntactically, values can be embedded (i.e.
  lexically in-line) or referenced (linked)
• Example

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Complex values (continued)

• Corresponding triples
• http//www.w3.org/TR/PR-rdf-syntax/,
  dcCreator, x
• x, pName, Ora Lassila
• x, pEMail, ora.lassila_at_nokia.com

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Containers

• Containers are collections
• they allow grouping of resources (or literal
  values)
• It is possible to make statements about the
  container (as a whole) or about its members
  individually
• Different types of containers exist
• bag - unordered collection
• seq - ordered collection ( sequence)
• alt - represents alternatives
• It is also possible to create collections based
  on URI patterns
• for example, all files in a particular web site
• Duplicate values are permitted
• there is no mechanism to enforce unique value
  constraints

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Containers (continued)
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Higher-order statements

• One can make RDF statements about other RDF
  statements
• example Ralph believes that the web contains
  one billion documents
• Higher-order statements
• allow us to express beliefs (and other
  modalities)
• are important for trust models, digital
  signatures,etc.
• also metadata about metadata
• are represented by modeling RDF in RDF itself

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Reification

• RDF is not really second-order
• But it does provide a built-in predicate
  vocabulary for reification

• The dotted box corresponds to the following
  statements
• x, rdfpredicate, dccreator
• x, rdfsubject, http//www.w3.org/TR/RED-rdf-sy
  ntax
• x, rdfobject, Ora Lassila
• x, rdftype, rdfstatement

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Reification

• Any statement can be an object
• graphs can be nested - reification

claims
NYT
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RDF Schema

• Defines small vocabulary for RDF
• Class, subClassOf, type
• Property, subPropertyOf
• domain, range
• Vocabulary can be used to define other
  vocabularies for your application domain

Person
subClassOf
subClassOf
range
domain
Student
Researcher
hasSuperVisor
type
type
Jeen
Frank
hasSuperVisor
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RDF Schema syntax in XML
ltrdfDescription ID"MotorVehicle"gt ltrdftype
resource"http//www.w3.org/...Class"/gt
ltrdfssubClassOf rdfresource"http//www.w3.org/.
..Resource"/gt lt/rdfDescriptiongt ltrdfDescriptio
n ID"Truck"gt ltrdftype resource"http//www.w
3.org/...Class"/gt ltrdfssubClassOf
rdfresource"MotorVehicle"/gt lt/rdfDescriptiongt
ltrdfDescription ID"registeredTo"gt
ltrdftype resource"http//www.w3.org/...Property
"/gt ltrdfsdomain rdfresource"MotorVehicle"/
gt ltrdfsrange rdfresource"Person"/gt lt/rdfD
escriptiongt ltrdfDescription IDownedBy"gt
ltrdftype resource"http//www.w3.org/...Property
"/gt ltrdfssubPropertyOf rdfresource"registe
redTo"/gt lt/rdfDescriptiongt
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Conclusions about RDF(S)
?

• Next step up from plain XML
• (small) ontological commitment to modeling
  primitives
• possible to define vocabulary
• However
• no precisely described meaning
• no inference model

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Beyond RDF OIL DAML

• OIL extends RDF Schema to a fully-fledged
  knowledge representation language.
• logical expressions
• data-typing
• cardinality
• quantifiers
• http//www.ontoknowledge.org
• DAML US sister of OIL
• Merged as DAMLOIL in 2001
• Becomes OWL W3C standard in March '03

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DAMLOIL (by example)
class-def animal animals are a
class class-def plant plants are a class
subclass-of NOT animal that is disjoint from
animals class-def tree subclass-of
plant trees are a type of plants class-def
branch slot-constraint is-part-of branches
are parts of some tree has-value tree
max-cardinality 1 class-def defined
carnivore carnivores are animals
subclass-of animal slot-constraint eats
that eat any other animals value-type
animal class-def defined herbivore
herbivores are animals subclass-of animal,
NOT carnivore that are not carnivores, and
slot-constraint eats they eat
plants or parts of plants value-type
plant OR (slot-constraint is-part-of has-value
plant)
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DAMLOIL as RDF(S) extension
ltrdfsClass rdfIDherbivoregt ltrdftype
rdfresourcehttp//www.ontoknowledge.org/
DefinedClass/gt ltrdfssubClassOf
rdfresourceanimal/gt ltrdfssubClassOfgt
ltoilNOTgt ltoilhasOperand
rdfresourcecarnivore/gt lt/oilNOTgt
lt/rdfssubClassOfgt lt/rdfsClassgt
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DAMLOIL as RDFS extension
RDF(S)
DAMLOIL

• class-def
• subclass-of
• slot-def
• subslot-of
• domain
• range

• class-expressions
• AND, OR, NOT
• slot-constraints
• has-value, value-type
• cardinality
• slot-properties
• trans, symm

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DAMLOIL Classes
ltdamlClass rdfID"Male"gt ltrdfssubClassOf
rdfresource"Animal"/gt lt/damlClassgt ltdamlCla
ss rdfID"Female"gt ltrdfssubClassOf
rdfresource"Animal"/gt ltdamldisjointWith
rdfresource"Male"/gt lt/damlClassgt ltdamlClass
rdfID"Man"gt ltrdfssubClassOf
rdfresource"Person"/gt ltrdfssubClassOf
rdfresource"Male"/gt lt/damlClassgt
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Class-Building Operations

• Relation to other Classes
• rdfssubClassOf
• damldisjointWith
• damldisjointUnionOf
• damlsameClassAs
• damlequivalentTo

• Contained Elements
• damloneOf
• Boolean combinations
• damlintersectionOf
• damlunionOf
• damlcomplementOf

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DAMLOIL Properties
ltdamlObjectProperty rdfID"hasParent"gt
ltrdfsdomain rdfresource"Animal"/gt
ltrdfsrange rdfresource"Animal"/gt lt/damlObje
ctPropertygt ltdamlObjectProperty
rdfID"hasChild"gt ltdamlinverseOf
rdfresource"hasParent"/gt lt/damlObjectProperty
gt ltdamlUniqueProperty rdfID"hasMother"gt
ltrdfssubPropertyOf rdfresource"hasP
arent"/gt ltrdfsrange rdfresource"Female"/gt
lt/damlUniquePropertygt
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Property-Building Operations

• Basic Types
• damlObjectProperty
• damlDataTypeProperty
• Special Types
• damlTransitiveProperty
• damlUniqueProperty
• damlUnambigousProperty
• Further Restrictions
• rdfssubPropertyOf
• rdfsdomain
• rdfsrange
• damlsamePropertyAs
• damlinverseOf

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DAMLOILProperty Restrictions
ltdamlClass rdfID"Person"gt ltrdfssubClassOf
rdfresource"Animal"/gt
ltrdfssubClassOfgt ltdamlRestrictiongt
ltdamlonProperty
rdfresource"hasFather"/gt ltdamltoClass
rdfresource"Man"/gt lt/damlRestrictiongt
ltdamlRestriction damlcardinality"1"gt
ltdamlonProperty rdfresource"hasFathe
r"/gt lt/damlRestrictiongt
lt/rdfssubClassOfgt lt/damlClassgt
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DAMLOILProperty Restrictions
ltdamlClass rdfID"Person"gt ltrdfssubClassOf
rdfresource"Animal"/gt
ltrdfssubClassOfgt ltdamlRestriction
damlcardinalityQ"1"gt ltdamlonProperty
rdfresource"hasFather"/gt
ltdamlhasClassQ rdfresource"Man"/gt
lt/damlRestrictiongt lt/rdfssubClassOfgt
lt/damlClassgt
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Restrictions

• General
• damlRestriction
• damlonProperty

• Number Restrictions
• damlcardinality
• damlmaxCardinality
• damlminCardinality

• Value and Type Restrictions
• damltoClass
• damlhasValue
• damlhasClass

• Combinations
• damlcardinalityQ
• damlmaxCardinalityQ
• damlminCardinalityQ

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Resources

• homepages.cwi.nl/lynda/spool/sw-tue-2003.ppt
• www.daml.org/meetings/2003/05/SWMU/briefings/
  07_1045_Essential_Building_Blocks.ppt
• www.ltg.ed.ac.uk/ht/ora-rdf-dagstuhl.ppt