An Introduction to the Semantic Web and Ontology Technology

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?????????? An Introduction to the Semantic Web
and Ontology Technology
??? Zhisheng Huang Vrije University Amsterdam The
Netherlands huang_at_cs.vu.nl
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?Google??starting from Google
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?????Existing Problems
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??????????Can we do it better?

• ???????Semantics-based search
• ?????? concept combination specification
• ?????? domain specific
• ???? approximate search
• ???? search agent

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???(Semantic Web)

• ??????????????????, ????
• The Semantic Web is an extension of the current
  web in which information is given well-defined
  meaning, better enabling computers and people to
  work in co-operation. Berners-Lee et al.,
  2001

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??????What is the Semantics?

• Frege(1848-1925) Reference and Sense
• Syntax, Semantics, Pragmatics
• Denotational Semantics vs. Operational Semantics
• Main features
• ??? (denotation)
• ???(uniqueness)
• ???(relatedness)

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????????(What the Semantic Web wants to do)

• ???????
• ?????
• Content is machine-understandable if it is bound
  to some formal description of itself (i.e.
  metadata).

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HTML??(HTML Markup)

• lth2gtZhisheng Huanglt/h2gt
• ltbgtAffiliationlt/bgt
• Department of Computer Scienceltbrgt
• Faculty of Sciencesltbrgt
• Vrije University Amsterdamltpgt
• ltbgtEmaillt/bgt huang _at_ cs.vu.nlltbrgt
• ltbgtPhonelt/bgt 31-20-4447740(office)
• lt/htmlgt

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XML?? XML-Annotations
ltresearchergtltnamegtZhisheng Huanglt/namegt ltaffiliati
ongt ltdepartmentgtDepartment of Computer
Sciencelt/departmentgt ltfacultygtFaculty of
Scienceslt/facultygt ltuniversitygtVrije University
Amsterdamlt/universitygt lt/affiliationgt ltemailgthuang
_at_ cs.vu.nllt/emailgt ltphone idofficegt
(31)-20-4447740lt/phonegt lt/researchergt lt/html
gt
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Data Structures

• ?????Structured Data
• Database
• ??????Semi-structured Data
• HTML, XML, BibTex
• ??????Non-structured Data
• Text

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??????XML??XML representation of a relational
database

• ltgroup nameAIgt
• ltmember id001gt
• ltnamegtJohnlt/namegt
• ltphonegt1234567lt/phonegt
• lt/membergt
• ltmember id002gt
• ltnamegtMarylt/namegt
• ltphonegt7654321lt/phonegt
• lt/membergt
• ..
• lt/groupgt

AI group
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??????Document Type Definition(DTD)

• lt!DOCTYPE researcher
• lt!ELEMENT researcher (name, affiliation, email,
  phone)gt
• lt!ELEMENT name (PCDATA)gt
• lt!ELEMENT email (PCDATA)gt
• lt!ELEMENT phone (PCDATA)gt
• lt!ATTLIST phone id CDATA REQUIRED gt
• lt!ELEMENT affiliation (department, faculty,
  university)gt
• gt

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????Data Model
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XML??XML Schema

• The purpose of an XML Schema is to define the
  legal building blocks of an XML document, just
  like a DTD.

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Why XML Schemas

• XML Schemas are extensible to future additions
• XML Schemas are richer and more useful than DTDs
• XML Schemas are written in XML
• XML Schemas support data types
• XML Schemas support namespaces

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????Name Conflicts

• Since element names in XML are not fixed, very
  often a name conflict will occur when two
  different documents use the same names describing
  two different types of elements.
• If these two XML documents were added together,
  there would be an element name conflict because
  both documents contain a same element with
  different content and definition.

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XML????XML NameSpace

• Using Namespaces to solve Name Conflicts
• Examples
• xmlnsnamespace prefix"namespace"
• xmlnsxsd"http//www.w3.org/2001/XMLSchema"

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????????? XML Schema
ltxsdelement name"reseracher"gt
ltxsdcomplexTypegt ltxsdelement name"name"
type"xsdString"/gt ltxsdelement
name"affiliation" type"affil" minOccurs"1"
maxOccurs"unbounded"/gt ltxsdelement
name"phone" type"xsdString"/gt ltxsdelement
name"email" type"xsdString"/gt
lt/xsdcomplexTypegt lt/xsdelementgt
ltxsdcomplexType name"affil"gt ltxsdelement
name " department" type"xsdString"/gt ltxsdelem
ent name " faculty" type"xsdString"/gt ltxsdele
ment name"university" type"xsdString"/gt
lt/xsdcomplexTypegt
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??????Resource Description Framework(RDF)

• Metadata is machine understandable information
  about web resources or anything that has an URI,
  it is represented as a set of independent
  assertions

ltrdfDescription about"http//wasp.cs.vu.nl/sekt/
dig/dig.pdf"gt ltdcCreator
rdfressource"http//www.cs.vu.nl/huang"/gt
ltdcCreator rdfressource"mailtoctv_at_cs.vu.n
l"/gt lt/rdfDescriptiongt
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RDF Dublin Core

• The Dublin Core provides properties for
  describing network objects, suitable for use by
  network search engines.
• The Dublin Core is a set of predefined properties
  for describing documents.
• The first Dublin Core properties were defined at
  the Metadata Workshop in Dublin, Ohio in 1995 and
  is currently maintained by the Dublin Core
  Metadata Initiative.

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Dublin Core Metadata Initiative

• The Dublin Core Metadata Initiative is an open
  forum engaged in the development of interoperable
  online metadata standards that support a broad
  range of purposes and business models.
• http//dublincore.org/

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Annotating Metadata

• ltrdfDescription rdfaboutdc-rdf/"gt
• ltdctitlegt
• Guidance on expressing the Dublin Core within
  the Resource
• Description Framework (RDF)
• lt/dctitlegt
• ltdccreatorgt Eric Miller lt/dccreatorgt
• ltdccreatorgt Paul Miller lt/dccreatorgt
• ltdccreatorgt Dan Brickley lt/dccreatorgt
• ltdcsubjectgt Dublin Core RDF XML
  lt/dcsubjectgt
• ltdcpublishergt Dublin Core Metadata
  Initiative lt/dcpublishergt
• ltdccontributorgt Dublin Core Data Model
  Working Group lt/dccontributorgt
• ltdcdategt 1999-07-01 lt/dcdategt
• ltdcformatgt text/html lt/dcformatgt
• ltdclanguagegt en lt/dclanguagegt
• lt/rdfDescriptiongt

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????????RDF Schema (RDFS)

• RDFS defines vocabulary for RDF
• Organizes this vocabulary in a typed hierarchy
• Class, subClassOf, type
• Property, subPropertyOf
• domain, range

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RDFS
Prof. Ma
Wang
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?????Concepts and Ontologies

• Philosophical discipline, branch of philosophy
  that deals with the nature and the organisation
  of reality.
• Science of Being (Aristotle, Metaphysics, IV,1)
• What is being?
• What are the features common to all beings?

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Vocabulary and Ontology

• Controlled vocabulary (Jernst 2003)
• a list of controlled terms
• unambiguous
• non-redundant definition
• Ontology a controlled vocabulary expressed in an
  ontology representation language (Jernst 2003)

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In computer science

• An ontology is an explicit specification of a
  conceptualization. Gruber93
• An ontology is a shared understanding of some
  domain of interest. Uschold, Gruninger96
• There are many definitions
• a formal specification EXECUTABLE
• of a conceptualization of a domain COMMUNITY
• of some part of world that is of interest
  APPLICATION
• Defines
• A common vocabulary of terms
• Some specification of the meaning of the terms
• A shared understanding for people and machines

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Why develop an ontology?

• To make domain assumptions explicit
• Easier to change domain assumptions
• Easier to understand and update legacy data
• To separate domain knowledge from operational
  knowledge
• Re-use domain and operational knowledge
  separately
• A community reference for applications
• To share a consistent understanding of what
  information means.

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???????Key features of an Ontology

• ?????Concept hierarchy,
• ??????concept subsumption

• ??????? InstanceOf Relation (Instances)

• ??????? PartOf Relation (property)

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Why not other alternatives

• ?????? the first-order predicate logic
• ??? set theory
• ???? programming languages

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RDF(S) Reconsideration

• Next step up from plain XML
• (small) ontological commitment to modeling
  primitives
• possible to define vocabulary
• However
• no precisely described meaning
• unclear semantics, no clean separation between
• Instances
• Concepts
• Meta-ontologies (e.g. RDFS language itself)
• no inference model

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??????Web Ontology Language (OWL)

• OWL is built on top of RDF
• OWL is for processing information on the web
• OWL was designed to be interpreted by computers
• OWL was not designed for being read by people
• OWL is written in XML
• OWL is a web standard

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Design Goals for OWL
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Layered language

• OWL Lite
• Classification hierarchy
• Simple constraints
• OWL DL
• Maximal expressiveness
• While maintaining tractability
• Standard formalisation
• OWL Full
• Very high expressiveness
• Loosing tractability
• Non-standard formalisation
• All syntactic freedom of RDF(self-modifying)

Full
DL
Lite
Syntactic layering Semantic layering
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OWL Example animals

• lt?xml version"1.0"?gtltrdfRDF
• xmlnsrdf"http//www.w3.org/1999/02/22-rdf-syntax
  -ns"
• xmlnsrdfs"http//www.w3.org/2000/01/rdf-sche
  ma"
• xmlnsowl"http//www.w3.org/2002/07/owl"
• xmlnsdc"http//purl.org/dc/elements/1.1/"
• xmlbase"http//wasp.cs.vu.nl/sekt/ontology/ani
  mal"gt
• ltowlOntology rdfaboutanimal"/gtltowlClass
  rdfID"Eagle"gt
• ltrdfssubClassOfgtltowlClass
  rdfabout"Bird"/gt
• lt/rdfssubClassOfgtlt/owlClassgtltowlClass
  rdfID"Animal"/gt
• ltowlClass rdfID"Fly"gtltowldisjointWithgt
• ltowlClass rdfabout"Penguin"/gtlt/owldisjo
  intWithgt
• ltrdfssubClassOf rdfresource"Animal"/gt
• lt/owlClassgtltowlClass rdfID"Bird"gt
• ltrdfssubClassOf rdfresource"Fly"/gt
• lt/owlClassgt
• ltowlClass rdfID"Penguin"gt
• ltrdfssubClassOf rdfresource"Bird"/gt
• ltowldisjointWith rdfresource"Fly"/gt
• lt/owlClassgt

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Semantic Web Layers
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????????Logical Foundation of the Semantic Web

• ???????????
• Description Logic vs. Frame-Logic
• ?????????????
• Closed world assumption vs. Open world assumption
• ????????????
• Unique name assumption vs. Non-unique name
  assumption
• ??????????
• Object-oriented vs. non-object oriented
• ..

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???? Description Logic
Knowledge Base
Tbox (schema)
Man Human u Male Happy-Father Man u 9
has-child Female u
Interface
Inference System
Abox (data)
John Happy-Father hJohn, Maryi has-child
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Basic Description Logic AL

• Concept Expressions
• A (atomic concept)
• ? (universal concept)
• ? (bottom concept)
• ? A (atomic negation)
• C ? D (intersection)
• ?R.C (value restriction)
• ?R.T (limited existential quantification)
• where A is a concept name, C and D are concept
  expressions, and R is a role expression

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Family of AL language

• C ? D (Union)
• ?R.C (Full Existential Quantification)
• ? C (Complement)
• Number restriction
• (? n R) (at least restriction)
• (? n R) (at most restriction)
• Qualified number restriction
• (? n R.C) (at least restriction)
• (? n R.C) (at most restriction)
• Transitive Role R
• Inverse of Role I
• Role Hierarchies R ?S H

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Examples

• woman person ? female
• man person ? ?woman
• mother woman ? ?hasChild.person
• father man ? ?hasChild.person

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Description Logics

• Decidable Subset of First-Order Logic
• Equivalent to 3 Variable Fragment (Borgida 1996)
• Model theoretic semantics by mapping to abstract
  domain
• Provides Primitives for defining Conceptual
  Knowledge
• Concept Expressions (Formulas with 1 free
  variable) for describing Sets of Objects
• Boolean Operators C?? D, C ? D, ?C
• Quantifiers (?R.C), (?P.C)
• Cardinality Constraints ( n R), (gt n R), (lt n
  R), (? n R), (? n R)
• Axioms define relations between concepts
• Subsumption C ? D
• Equivalence C ? D
• Disjointness C ?? D ? ?

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DL Semantics

• Interpretation function extends to concept
  expressions in an obvious(ish) way, i.e.

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DL for OWL SHIQ

• SHIQ ALCQHIR

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Frame-logic (F-logic)

• Object oriented
• Frame based
• Rule-based
• Negation as failure

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Example

• / facts /
• abrahamman.
• sarahwoman.
• isaacmanfather-gtabraham mother-gtsarah.
• ishmaelmanfather-gtabraham mother-gthagarwoman.
  
• jacobmanfather-gtisaac mother-gtrebekahwoman.
• esaumanfather-gtisaac mother-gtrebekah.
• / rules consisting of a rule head and a rule
  body /
• FORALL X,Y Xson-gtgtY lt- Ymanfather-gtX.
• FORALL X,Y Xson-gtgtY lt- Ymanmother-gtX.
• FORALL X,Y Xdaughter-gtgtY lt- Ywomanfather-gtX.
• FORALL X,Y Xdaughter-gtgtY lt- Ywomanmother-gtX.
• / query /
• FORALL X,Y lt- Xwomanson-gtgtYfather-gtabraham.

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Semantic Web Application the foaf project

• The Friend of a Friend (FOAF) project is about
  creating a Web of machine-readable homepages
  describing people, the links between them and the
  things they create and do.
• http//www.foaf-project.org/

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Foaf.rdf

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltrdfRDF
• xmlnsfoaf"http//xmlns.com/foaf/0.1/"
• xmlnsrdf"http//www.w3.org/1999/02/22-rdf-synt
  ax-ns"
• xmlnsrdfs"http//www.w3.org/2000/01/rdf-schema
  "gt
• ltfoafPersongt
• ltfoafsurnamegtHuanglt/foafsurnamegt
• ltfoafnamegtZhisheng Huanglt/foafnamegt
• ltfoaffirstNamegtZhishenglt/foaffirstNamegt
• ltfoafgendergtmalelt/foafgendergt
• ltfoafimg rdfresource"http//wasp.cs.vu.nl/hu
  ang/images/huang02.jpg" /gt
• ltfoafhomepage rdfresource"http//wasp.cs.vu.n
  l/huang/" /gt
• ltfoafmbox_sha1sumgt238a59a17bd96fbb93f39aa9dba2f
  6847a8d261clt/foafmbox_sha1sumgt
• ltfoafworkplaceHomepage rdfresource"http//www
  .vu.nl/" /gt
• ltfoafmboxgtmailtohuang_at_cs.vu.nllt/foafmboxgt
• ltfoafknowsgt
• ltfoafPersongt
• ltfoafnamegtAnnette ten Teijelt/foafnamegt
• ltfoafmbox_sha1sumgtc10984c365331f1d38f649adc
  cbb7aac5873aed2lt/foafmbox_sha1sumgt

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Add the FOAF information on the homepage

• lthtmlgt ltheadgt ...
• ltlink rel"meta type"application/rdfxml"
  title"FOAF" href"foaf.rdf" /gt
• lt/headgt ltbodygt ... lt/bodygt lt/htmlgt
• FOAF Agents on the Internet will now be able to
  locate the FOAF entry.

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FOAFBot IRC Community Support Agent

• FOAFBot is an IRC bot that provides access to a
  knowledge base created by spidering FOAF files.
• It can sit on an IRC channel and provide basic
  informational help about the members of a
  community.

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DOPE

• The DOPE Browser is a deliverable created by
  Aduna BV for the Drug Ontology Project for
  Elsevier (DOPE), a project funded by the Elsevier
  Advanced Technology Group.

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Variants of ontologies

• ??????? Domain ontology domain specific
  ontology.
• Upper Ontology limited to concepts that are
  meta, generic, abstract and philosophical,
  general enough to address (at a high level) a
  broad range of domain areas.

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Suggested Upper Merged Ontology (SUMO)

• http//www.ontologyportal.org/
• SUMO is written in the SUO-KIF language
• Largest free, formal ontology available, with
  20,000 terms and 60,000 axioms when all domain
  ontologies are combined.

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SUMO

• These consist of SUMO itself, the MId-Level
  Ontology (MILO), and ontologies of
• Communications
• Countries and Regions
• Distributed computing,
• Economy
• Finance,
• Engineering components
• Geography,
• Government,
• Military,
• People
• Transportation

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????Gene Ontology

• http//www.geneontology.org/
• Controlled vocabulary to describe gene and gene
  product attributes in any organism.
• Updated every 30 minutes
• 9759 biological_process1574 cellular_component70
  76 molecular_function (up to 16/8/2005)
• Format Obo, GO, OWL

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?????????SEKT Project

• Semantically Enabled Knowledge Technologies
  (SEKT)
• A European research and development project
  launched under the EU Sixth Framework Programme.
• .

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Duration and Partners

• Three year project January 2004 December 2006.
• 13 partners
• ?? BT(????), Empolis GmbH, iSOCO(Spain), Kea-pro
  GmbH, Ontoprise, Sirma AI EOOD(Bulgaria),
  (SIEMENS?????)
• ?? Jozef Stefan Institute(Slovenia), Univ.
  Karlsruhe(Germany), Univ. Sheffield(U.K.), Univ.
  Innsbruck(O), Univ. Autonoma Barcelona(Spain),
  Vrije Universteit Amsterdam(The Netherlands)

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Case Studies

• Legal Domain (iSOCO)
• Telecom Domain (BT)
• Siemens

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SEKT Activities and Relationships
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Core Tasks WP3
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Main Goals of WP3

• Enable and greatly facilitate setting up, usage
  and maintenance of Ontologies and related
  Metadata
• Combine manual and (semi-) automatic approaches
  for evolution of Ontologies and related Metadata
• Make extensive use of reasoning

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Task Overview

• Incremental Ontology Evolution
• Usage Tracking for Ontologies and Metadata
• Data-driven Change Discovery
• Reasoning with inconsistent Models
• Multi-Version Reasoning
• Inconsistency Diagnosis and Repair

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WP3.4 Reasoning with Inconsistency

• Milestone 3.4 Software Prototypes
• D3.4.1 Reasoning with Inconsistent Models. V1.
  P/PU/Month 12

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What We are Expecting

• Given an inconsistent ontology, return meaningful
  partial answers to queries (given that fully
  logically correct answers are not possible)
• Use nonstandard reasoning to deal with
  inconsistency

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WP3.5 Multi-Version Reasoning

• Main task given two versions of an ontology and
  a query, indicate how the changes in the ontology
  have affected the answer to the query.
• Milestone 3.5 Software Prototypes
• D3.5.1 Multi-version reasoning V1. P/PU/Month 18

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WP3.6 Inconsistency Diagnosis and Repair

• Main task given an inconsistent ontology, locate
  possible sources of inconsistencies and offer
  them to the user (a knowledge engineer) for
  repair.
• Milestone 3.6 Software Prototypes
• D3.6.1 Inconsistency Diagnosis and Repair V1.
  P/PU/Month 21

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Topics in Ontology Management

• Ontology reasoning
• Ontology change and evolution
• Ontology merge
• Ontology mapping
• Multi-version ontology reasoning and management
• Inconsistent ontology processing