语义网与本体技术导论

1、语义网与本体技术导论 An Introduction to the Semantic Web and Ontology Technology 黄智生Zhisheng HuangVrije University AmsterdamThe Netherlands语义网与本体技术系列讲座第一部分：导论2009年9月9日星期三14：00-15：30第二部分：逻辑基础2009年9月12日星期六10：00-11：30第三部分：专题研究2009年9月13日星期日14：00-15：30万维网: 影响和展望WWW: Its impacts and visions从Google谈起starting from Go

2、ogle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 informati

3、on 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 SenseSyntax, Semantics, PragmaticsDenotational Semantics vs. Operational SemanticsMain features指称性 (denotation)唯一性(uniqu

4、eness)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)Zhisheng HuangAffiliation: Department of Computer ScienceFaculty of SciencesVrije University Amsterdam

5、Email: huang cs.vu.nlPhone: 31-20-4447740(office)XML标注XML-AnnotationsZhisheng HuangDepartment of Computer ScienceFaculty of SciencesVrije University Amsterdamhuang cs.vu.nl (31)-20-4447740Data 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 Dat

6、a:Text关系数据库的XML表示XML representation of a relational databaseJohn1234567Mary7654321.AI group文件类型定义Document Type Definition(DTD)!DOCTYPE researcher XML模式XML SchemaThe purpose of an XML Schema is to define the legal building blocks of an XML document, just like a DTD. Why XML SchemasXML Schemas are ext

7、ensible 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 ConflictsSince element names in XML are not fixed, very often a name conflict will occur when two different documents use

8、 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 NameSpaceUsing Namespaces to solve Name ConflictsExample

9、s:xmlns:namespace prefix=namespace xmlns:xsd= 可扩展标识语言模式XML Schema 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:ZhishengCreatorCeesCreatorTriple: T(subject,

10、 attribute, values) RDF: Dublin CoreThe 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 Dubl

11、in, Ohio in 1995 and is currently maintained by the Dublin Core Metadata Initiative.Dublin Core Metadata InitiativeThe 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. An

12、notating Metadata Guidance on expressing the Dublin Core within the Resource Description Framework (RDF) Eric Miller Paul Miller Dan Brickley Dublin Core; RDF; XML Dublin Core Metadata Initiative Dublin Core Data Model Working Group 1999-07-01 text/html en 资源描述框架模式RDF Schema (RDFS)RDFS defines vocab

13、ulary for RDFOrganizes this vocabulary in a typed hierarchyClass, subClassOf, typeProperty, subPropertyOfdomain, rangeRDFSProf. ZhongZeng，YiPersonPhDStudentProfessorsubClassOfsubClassOftypehasSuperVisordomainrangetype概念与本体Concepts and OntologiesPhilosophical discipline, branch of philosophy that dea

14、ls 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 termsunambiguousnon-redundant definitionOntology: a controlled

15、 vocabulary expressed in an ontology representation language (Jernst 2003)In computer science An ontology is an explicit specification of a conceptualization. Gruber93An ontology is a shared understanding of some domain of interest. Uschold, Gruninger96There are many definitionsa formal specificatio

16、n EXECUTABLEof a conceptualization of a domain COMMUNITYof some part of world that is of interest APPLICATIONDefinesA common vocabulary of termsSome specification of the meaning of the termsA shared understanding for people and machinesWhy develop an ontology?To make domain assumptions explicitEasie

17、r to change domain assumptionsEasier to understand and update legacy dataTo separate domain knowledge from operational knowledgeRe-use domain and operational knowledge separatelyA community reference for applicationsTo share a consistent understanding of what information means.本体的主要特征Key features of

18、 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网络本体语言Web Ontology Language (OWL)OWL is built on top of RDF OW

19、L 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 OWLLayered language OWL Lite:Classification hierarchySimple constraints OWL DL:Maximal expressivenessW

20、hile maintaining tractabilityStandard formalisation OWL Full:Very high expressivenessLoosing tractabilityNon-standard formalisationAll syntactic freedom of RDF(self-modifying)Syntactic layeringSemantic layeringFullDLLiteOWL Example: animals 网络1.0 Web1.0网络2.0 Web2.0对网络3.0的期待Expectations on Web3.0新颖性(

21、Novelty)： 它不同于已有的Web1.0和Web2.0的技术，它能提供全新的一代网络服务模式(即为什么不是Web1.0或Web2.0）从字面上看对Web3.0的特征期待：可行性(Achievability)：它在现有的网络环境下，经过努力是可能实现的， 它并不存在不可逾越的技术障碍（即为什么不是Web4.0或更高）。 迫切性(Urgency)：它提供网络服务是当前社会迫切需要的，它的技术引入是能够对社会产生重大影响。（即为什么只能是Web3.0）网络3.0 Web3.0网络1.0 网络2.0 网络3.0Web1.0 Web2.0 Web3.0网络1.0： 文件网 Web1.0: Web

22、of documents网络2.0： 人际/社会网 Web2.0: Web of persons网络3.0： 数据网 Web3.0: Web of data (semantics)网络发展整体观语义联接的好处：从一个实例说起Advantages of Linked Data数据联接的好处：小结现有的网页是供人们阅读的，不便于机器自动处理，数据联接便于机器自动处理文件联接在局部文字上只允许一个链接，而数据联接对局部文字支持多重链接文件联接只提供部分文字链接，而数据联接保证全文链接基于关键词的搜索引擎如Google虽然看起来支持全文检索，但它不能区分同一个词的不同含义，这对于人名，地名等重复性频率

23、较高的问题领域处理尤其困难，而且在许多具体应用领域一词多义的情形比比皆是。数据联接的统一概念格式三元组(Triple)方法: 例子：提供网络资源的描述能力例子：提供语义的唯一标识让数据内容独立于表达形式提供初步的语义推理能力为什么推理支持是必要的？例子：从ZhishengHuang是自由大学的雇员和自由大学在阿姆斯特丹，能够推出ZhishengHuang在阿姆斯特丹工作。, -=语义网与本体Semantic Web and Ontologies五句话介绍语义网的主要思想： Why the Semantic Web？任任何信息系统都需要数据；数数据表示要独立于具体的应用和平台，以保证最大程度地可

24、重用；采用统一的数据概念表示以保证数据表示独立于具体系统（即可采用Triple/Tuple形式） ；数数据应能描述网络资源（即要采用RDF/RDFS或其他类似的语言）数数据应提供初步的推理支持（即要采用OWL或其他知识表示语言）（注意；RDF/RDFS/OWL均采用Triple语义模型） 发展趋势根据美国著名市场研究公司Gartner的2007五月份报告， 到2012年，70%的公开网页将带有一定程度的语义标注，20%将使用更强的基于语义网的本体。Gartner (May 2007):By 2012, 70% of public Web pages will have some level o

25、f semantic markup, 20% will use more extensive Semantic Web-based ontologies”海量语义数据的一部分Ontologies and Metadata: Billion Triples dataset（十亿三元组数据集）雅虎数据东南大学数据马里兰大学英国open大学SemWebBase（DERI)维基百科地理名字出版物英文语义词典Freebase美国政府数据Linked Data 2009一个具体的数据联接的实例一个具体的数据联接的实例Falcons让数据内容独立于表达形式Semantic Web Layers语义网的逻辑基

26、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.一个实例王老师有孩子：王一， 王二，王三。问：王老师有几个孩子？封闭世界与唯一名

27、： 3 个开放世界与唯一名：至少3个开放世界与非唯一名：至少1个思考：在网络环境下，哪种方式比较合适？语义网应用的一些实例：DBpedia Mobile芬兰医疗语义网HealthFinland Health Information on the Semantic Webprovide a new kind of solution approach to these problems on a national Finnish level. The system consists of three main components: Metadata, ontology, and service

28、infrastructure. Semantic content creation process. A content creation and harvesting system has been implemented for producing semantically annotated contents, based on the shared metadata model and ontologies. Semantic portal HealthFinland (TerveSuomi) and its services. The material is published via a semantic portal that creates a single national entry-point for health information, health promotion and health-related news. National Semantic Web Ontology Project in Finland (FinnONTO), Na