27/07/2004 语义支撑的知识技术 Semantically Enabled Knowledge Technologies - 论语义网的影响－ On the impacts of the Semantic Web 黄智生（ Zhisheng

27/07/2004 http://sekt.semanticweb.org/ 1

语义支撑的知识技术 Semantically Enabled Knowledge Technologies

- 论语义网的影响－ On the impacts of the Semantic Web

黄智生（ Zhisheng Huang)

Vrije University Amsterdam

The Netherlands

[email protected]


语义网 (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]


从 Google 谈起


存在的问题


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 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-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>


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)>… ]>


DTD: Formal Model

• DTDs are context-free grammars.

• A DTD is a tuple (d, sd) where d is a function that maps symbols in a finite alphabet to regular expressions over

and sd is the start symbol.


Researcher Affiliation

hasDepartment

Faculty

University

Name

Phone

eMail

1n

Data Model


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


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 NameSpace

• Using Namespaces to solve Name Conflicts

Examples:

• xmlns:namespace prefix="namespace"

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


XML Schema – Data Models for the Web

<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>


RDF(Resource Description Framework) – A Data Model for Metadata

• 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/


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>


RDF Schema (RDFS)

• RDFS defines vocabulary for RDF

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


RDFS

ChenXiaoping

ZhouYi

Person

PhDStudent Professor

subClassOfsubClassOf

type

hasSuperVisordomain range

type


Concepts and Ontologies

• Semantics – the meaning of meaning.

• 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?


Origin and History

“Jaguar“

Concept

[Ogden, Richards, 1923]

• Humans require words (or at least symbols) to communicate efficiently. The mapping of words to things is only indirect possible. We do it by creating concepts that refer to things.

• The relation between symbols and things has been described in the form of the meaning triangle:


Ontology: Definition

• When talking about an ontology it is important to have a common definition on what one is talking about.

• Unfortunally:• The problem of exactly defining what an

ontology is hasn‘t been solved by the community.

• The relation between ontology and knowledge base is also a point of discussion.


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


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• unclear semantics, no clean separation between:

• Instances• Concepts• Meta-ontologies (e.g. RDFS language itself)

• no inference model


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.



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: animal

<?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=""/><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


Logical Foundationd of the Semantic Web

• Description Logic vs. F-Logic• Closed world assumption vs. Open world

assumption• Unique name assumption vs. Non-

unique name assumption• Object-oriented vs. non-object oriented• …..


Short History of Description Logics

• Phase 1:• Incomplete systems (Back, Classic, Loom, . . . )• Based on structural algorithms

• Phase 2:• Development of tableau algorithms and complexity results• Tableau-based systems for Pspace logics (e.g., Kris, Crack)• Investigation of optimisation techniques

• Phase 3:• Tableau algorithms for very expressive DLs• Highly optimised tableau systems for ExpTime logics (e.g.,

FaCT, DLP, Racer)• Relationship to modal logic and decidable fragments of

FOL


DL Architecture

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: ALC

• Axioms:• C ⊑ D C ≡ D• where C and D are concept expressions

• Concept Expressions:

• CN ⊤ C C ⊓ D C ⊔ D R.C R.C• where CN is a concept name, C and D are

concept expressions, and R is a role expression

• Role Expressions are of the form RN, where RN is a role name


Examples

woman ≡ person ⊓ female

man ≡ person ⊓ woman

mother ≡ woman ⊓ hasChild.person

father ≡ man ⊓ hasChild.person


DL Knowledge Base• DL Knowledge Base (KB) normally separated into 2 parts:

• TBox is a set of axioms describing structure of domain (i.e., a conceptual schema), e.g.:

• HappyFather Man hasChild.Female …• Elephant Animal Large Grey

• transitive(ancestor)

• ABox is a set of axioms describing a concrete situation (data), e.g.:

• John:HappyFather

• <John,Mary>:hasChild

• Separation has no logical significance

• But may be conceptually and implementationally convenient


• 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


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: Applications


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 Your 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.

http://xmlns.com/foaf/0.1


SEKT Project

• Semantically Enabled Knowledge Technologies (SEKT)

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

• The total budget is 12.5 M euros.


SEKT Project: Vision

• To delevop and exploit the knowledge technologies wich underlie Next Generation Knowledge management.

• SEKT will deliver software to: • semi-automatically learn ontologies and

extract metadata,• maintain and evolve the ontologies and

metedata over time• provide knowledge access• ……


Duration and Partner

• Three year project: January 2004 – December 2006.

• 13 partners: BT, Empolis GmbH, Jozef Stefan Institute, Univ. Karlsruhe, Univ. Sheffield, Univ. Innsbruck, iSOCO(Spain), Kea-pro GmbH, Ontoprise, Sirma AI EOOD(Bulgaria), Univ. Autonoma Barcelona, and VUA


Case Studies

• Media Domain (Empolis)

• Legal Domain (iSOCO)

• Telecom Domain (BT)


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


Thanks

• Frank van Harmelen, • Heiner Stuckenschmidt• Marc Ehrig• W3schools• …..

Some material in this PPT come from their presentations at SEKT meetings and others

Documents

27/07/2004 语义支撑的知识技术 Semantically Enabled Knowledge Technologies - 论语义网的影响 － On the impacts of the Semantic Web 黄智生（ Zhisheng

27/07/2004 语义支撑的知识技术 Semantically Enabled Knowledge Technologies - 论语义网的影响－ On the impacts of the Semantic Web 黄智生（ Zhisheng