China 2005 语义网与本体技术导论 An Introduction to the Semantic Web and Ontology...

China 2005 http://sekt.semanticweb.org/ 1

语义网与本体技术导论 An Introduction to the Semantic Web and Ontology

Technology

黄智生

Zhisheng Huang

Vrije University Amsterdam

The Netherlands

[email protected]


从 Google 谈起starting from Google


存在的问题Existing Problems


我们能不能做得更好？Can we do it better?

• 基于语义的搜索 Semantics-based search• 概念组合描述 concept combination

specification• 指定特定领域 domain specific• 逼近搜索 approximate search• 搜索代理 search agent


语义网 (Semantic Web)

•核心思想 : 给网络信息赋于确切定义的意义 , 即语义。„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]


语义是什么 ?What is the Semantics?

• Frege(1848-1925): Reference and Sense• Syntax, Semantics, Pragmatics• Denotational Semantics vs. Operational Semantics

Main features• 指称性 (denotation)• 唯一性 (uniqueness)• 相关性 (relatedness)


语义网想做什么？(What the Semantic Web wants

to do)

• 机器可自动处理• 机器可理解Content is machine-understandable if it

is bound to some formal description of itself (i.e. metadata).

HTML 标识 (HTML Markup)……<h2>Zhisheng Huang</h2>Affiliation: Department of Computer Science Faculty of Sciences Vrije University AmsterdamEmail: huang @ cs.vu.nl Phone: 31-20-4447740(office)……

</html>

XML标注XML-Annotations

<researcher><name>Zhisheng Huang</name><affiliation><department>Department of Computer

Science</department><faculty>Faculty of Sciences</faculty><university>Vrije University Amsterdam</university></affiliation><email>huang @ cs.vu.nl</email><phone id=“office”> (31)-20-4447740</phone>……</researcher>

</html>


Data Structures

• 结构化数据 Structured Data:• Database

• 半结构化数据 Semi-structured Data:• HTML, XML, BibTex

• 非结构化数据 Non-structured Data:• Text

关系数据库的 XML表示XML representation of a

relational database<group name=“AI”><member id=“001”><name>John</name><phone>1234567</phone></member><member id=“002”><name>Mary</name><phone>7654321</phone></member>…..</group>

member id name phone

001 John 1234567

002 Mary 7654321

… … …

AI group

文件类型定义Document Type Definition(DTD)

<!DOCTYPE researcher [<!ELEMENT researcher (name, affiliation, email,

phone)><!ELEMENT name (#PCDATA)><!ELEMENT email (#PCDATA)><!ELEMENT phone (#PCDATA)>

<!ATTLIST phone id CDATA #REQUIRED ><!ELEMENT affiliation (department, faculty,

university)>… ]>


Researcher Affiliation

hasDepartment

Faculty

University

Name

Phone

eMail

1n

数据模型 Data Model


XML 模式 XML Schema

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


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


名字冲突 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.


XML 名字空间 XML NameSpace

• Using Namespaces to solve Name Conflicts

Examples:

• xmlns:namespace prefix="namespace"

• xmlns:xsd="http://www.w3.org/2001/XMLSchema"

可扩展标识语言模式XML Schema

<xsd:element name="reseracher"> <xsd:complexType>

<xsd:element name="name" type="xsd:String"/><xsd:element name="affiliation" type="affil"

minOccurs="1" maxOccurs="unbounded"/><xsd:element name="phone" type="xsd:String"/><xsd:element name="email" type="xsd:String"/>

</xsd:complexType> </xsd:element> <xsd:complexType name="affil">

<xsd:element name= " department" type="xsd:String"/><xsd:element name= " faculty" type="xsd:String"/><xsd:element name="university" type="xsd:String"/>

</xsd:complexType>

资源描述框架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:

http://wasp.cs.vu.nl/sekt/dig/dig.pdf

ZhishengCreator

CeesCreator

Triple: T(subject, attribute, values)

<rdf:Description about="http://wasp.cs.vu.nl/sekt/dig/dig.pdf"> <dc:Creator rdf:ressource="http://www.cs.vu.nl/~huang"/> <dc:Creator rdf:ressource="mailto:[email protected]"/> </rdf:Description>


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.

http://dublincore.org/

http://dublincore.org/


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/

Annotating Metadata

<rdf:Description rdf:about=…dc-rdf/"> <dc:title>

Guidance on expressing the Dublin Core within the Resource Description Framework (RDF)

</dc:title> <dc:creator> Eric Miller </dc:creator> <dc:creator> Paul Miller </dc:creator> <dc:creator> Dan Brickley </dc:creator> <dc:subject> Dublin Core; RDF; XML </dc:subject> <dc:publisher> Dublin Core Metadata Initiative

</dc:publisher> <dc:contributor> Dublin Core Data Model Working

Group </dc:contributor> <dc:date> 1999-07-01 </dc:date> <dc:format> text/html </dc:format> <dc:language> en </dc:language> </rdf:Description>


资源描述框架模式RDF Schema (RDFS)

• RDFS defines vocabulary for RDF

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


RDFS

Prof. MaWang

Person

Student Professor

subClassOfsubClassOf

type

hasSuperVisordomain range

type


概念与本体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?


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)


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


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.


本体的主要特征Key features of an

Ontology• 概念层次性 Concept hierarchy,

• 概念包含关系 concept subsumption

•特殊与一般关系 InstanceOf Relation (Instances)

•部分与整体关系 PartOf Relation (property)


Why not other alternatives

• 一阶谓词逻辑 the first-order predicate logic

• 集合论 set theory

• 程序语言 programming languages


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


网络本体语言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


Design Goals for OWL


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) Syntactic layeringSemantic layering

Syntactic layeringSemantic layering

Full

DL

Lite

OWL Example: animals

<?xml version="1.0"?><rdf:RDFxmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:owl="http://www.w3.org/2002/07/owl#" xmlns:dc="http://purl.org/dc/elements/1.1/" xml:base="http://wasp.cs.vu.nl/sekt/ontology/animal"> <owl:Ontology rdf:about=“animal"/><owl:Class rdf:ID="Eagle"> <rdfs:subClassOf><owl:Class rdf:about="#Bird"/> </rdfs:subClassOf></owl:Class><owl:Class rdf:ID="Animal"/> <owl:Class rdf:ID="Fly"><owl:disjointWith> <owl:Class rdf:about="#Penguin"/></owl:disjointWith> <rdfs:subClassOf rdf:resource="#Animal"/> </owl:Class><owl:Class rdf:ID="Bird"> <rdfs:subClassOf rdf:resource="#Fly"/> </owl:Class> <owl:Class rdf:ID="Penguin"> <rdfs:subClassOf rdf:resource="#Bird"/> <owl:disjointWith rdf:resource="#Fly"/> </owl:Class></rdf:RDF>


Semantic Web Layers


语义网的逻辑基础Logical Foundation of the Semantic

Web

描述逻辑与框架逻辑之争Description Logic vs. Frame-Logic

• 封闭世界假说与开放世界假说Closed world assumption vs. Open world assumption• 唯一名假说与非唯一名假说Unique name assumption vs. Non-unique name assumption• 面向对象与非面向对象Object-oriented vs. non-object oriented• …..


描述逻辑 Description Logic

Knowledge Base

Tbox (schema)

Abox (data)

Man ´ Human u Male

Happy-Father ´ Man u 9 has-child Female u …

John : Happy-Father

hJohn, Maryi : has-child Infe

ren

ce S

yste

m

Inte

rface


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


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


Examples

woman ≡ person ⊓ female

man ≡ person ⊓ woman

mother ≡ woman ⊓ hasChild.person

father ≡ man ⊓ hasChild.person

• 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), (> n R), (< n R), ( n R), ( n R)

• Axioms define relations between concepts• Subsumption: C D • Equivalence: C D• Disjointness: C D

Description Logics


DL Semantics• Interpretation function extends to

concept expressions in an obvious(ish) way, i.e.:


DL for OWL: SHIQ

• SHIQ = ALCQHIR+


Frame-logic (F-logic)

• Object oriented

• Frame based

• Rule-based

• …

• Negation as failure

Example

/* facts */abraham:man.sarah:woman.isaac:man[father->abraham; mother->sarah].ishmael:man[father->abraham; mother->hagar:woman].jacob:man[father->isaac; mother->rebekah:woman].esau:man[father->isaac; mother->rebekah].

/* rules consisting of a rule head and a rule body */FORALL X,Y X[son->>Y] <- Y:man[father->X].FORALL X,Y X[son->>Y] <- Y:man[mother->X].FORALL X,Y X[daughter->>Y] <- Y:woman[father->X].FORALL X,Y X[daughter->>Y] <- Y:woman[mother->X]./* query */FORALL X,Y <- X:woman[son->>Y[father->abraham]].


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/

Foaf.rdf

<?xml version="1.0" encoding="UTF-8"?><rdf:RDF xmlns:foaf="http://xmlns.com/foaf/0.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"><foaf:Person> <foaf:surname>Huang</foaf:surname> <foaf:name>Zhisheng Huang</foaf:name> <foaf:firstName>Zhisheng</foaf:firstName> <foaf:gender>male</foaf:gender> <foaf:img rdf:resource="http://wasp.cs.vu.nl/~huang/images/huang02.jpg" /> <foaf:homepage rdf:resource="http://wasp.cs.vu.nl/~huang/" /> <foaf:mbox_sha1sum>238a59a17bd96fbb93f39aa9dba2f6847a8d261c</foaf:mbox_sha1sum> <foaf:workplaceHomepage rdf:resource="http://www.vu.nl/" /> <foaf:mbox>mailto:[email protected]</foaf:mbox> <foaf:knows> <foaf:Person> <foaf:name>Annette ten Teije</foaf:name> <foaf:mbox_sha1sum>c10984c365331f1d38f649adccbb7aac5873aed2</foaf:mbox_sha1sum> </foaf:Person> </foaf:knows> <foaf:knows> <foaf:Person>……

Add the FOAF information on the homepage

<html> <head> ...

<link rel="meta“ type="application/rdf+xml" title="FOAF" href="foaf.rdf" />

</head> <body> ... </body> </html>

• FOAF Agents on the Internet will now be able to locate the FOAF entry.


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.


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.


Variants of ontologies

• 具体领域的本体 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.


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.

http://www.ontologyportal.org/

http://cvs.sourceforge.net/viewcvs.py/*checkout*/sigmakee/sigma/suo-kif.pdf?rev=1.4


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


基因本体 Gene Ontology

• http://www.geneontology.org/• Controlled vocabulary to describe gene

and gene product attributes in any organism.

• Updated every 30 minutes • 9759 biological_process

1574 cellular_component7076 molecular_function (up to 16/8/2005)

• Format: Obo, GO, OWL


语义网核心研究课题：SEKT Project

• Semantically Enabled Knowledge Technologies (SEKT)

• A European research and development project launched under the EU Sixth Framework Programme.

.


Duration and Partners

• Three year project: January 2004 – December 2006.

• 13 partners:公司： BT( 英国电信 ), Empolis GmbH,

iSOCO(Spain), Kea-pro GmbH, Ontoprise, Sirma AI EOOD(Bulgaria), (+SIEMENS 西门子公司 )

大学： Jozef Stefan Institute(Slovenia), Univ. Karlsruhe(Germany), Univ. Sheffield(U.K.), Univ. Innsbruck(O), Univ. Autonoma Barcelona(Spain), Vrije Universteit Amsterdam(The Netherlands)


Case Studies

• Legal Domain (iSOCO)

• Telecom Domain (BT)

• Siemens


SEKT Activities and Relationships


Core Tasks: WP3


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

AIF

B


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

AIF

B


WP3.4 Reasoning with Inconsistency

• Milestone 3.4 – Software Prototypes• D3.4.1: Reasoning with Inconsistent Models. V1.

P/PU/Month 12


• 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

What We are Expecting


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


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


Topics in Ontology Management

• Ontology reasoning

• Ontology change and evolution

• Ontology merge

• Ontology mapping

• Multi-version ontology reasoning and management

• Inconsistent ontology processing

China 2005 语义网与本体技术导论 An Introduction to the Semantic Web and Ontology...

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