An Introduction to Semantic Web Portal Ching-Long Yeh

An Introduction to Semantic Web Portal Ching-Long Yeh 葉慶隆 Department of Computer Science and Engineering Tatung University chingyeh@cse. ttu. edu. tw http: //www. cse. ttu. edu. tw/chingyeh Semantic Web Portal

Outline • • • A brief description to the Semantic Web Portal Architectural basis of the Semantic Web KA 2: an ontology-based web portal An architecture of RDF triple data store Conclusions Semantic Web Portal 2

Introduction to Semantic Web • Facilities to put machine-understandable data on the Web are becoming a high priority for many communities. • The Web can reach its full potential only if it becomes a place where data can be shared and processed by automated tools as well as by people. • For the Web to scale, tomorrow's programs must be able to share and process data even when these programs have been designed totally independently. Semantic Web Portal 3

Introduction to Semantic Web • The Semantic Web is a vision: the idea of having data on the web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications • See “W 3 C Semantic Web Activity, ” by Marja-Riitta Koivunen, for more descriptions. Semantic Web Portal 4

The Semantic Web Layered Architecture Proof Tim Berners-Lee: “Axioms, Architecture and Aspirations” W 3 C all-working group plenary Meeting 28 February 2001 (http: //www. w 3. org/2001/T alks/0228 -tbl/slide 5 -0. html) Logic Rules Ontology Sig RDF Schema RDF M&S XML Schema XML URI Semantic Web Portal Namespaces Unicode 5

AI’s Chance Namespaces • Increasing demand formalized knowledge on the Web: AI’s chance! • XML- & RDF-based markup languages provide a 'universal' storage/interchange format for such Webdistributed knowledge representation. CSS DTDs DAML XSLT Stylesheets Agents Ontobroker Horn. ML Rules Transformations XML XQL Queries XQuery XML-QL SHOE Frames RDF[S] Acquisition Topic. Maps Protégé Semantic Web Portal 6

The Big Picture of SW Semantic Web Portal 7

Web Portals • A web portal is a web site that provides information content on a common topic. – General portals, e. g. , Yahoo, Excite, Netscape, Lycos, CNET, MSN, and AOL. com – Specialized portal e. g. , gardeners. com, semanticweb. org • Making valuable information to be found – – directory service, search facility news, e-mail, community forum Semantic Web Portal 8

Ontology-Based Web Portals • Ontology represents – common knowledge and interests sharing within their community • Tasks that ontology can be used to support a portal – Accessing a portal • Conceptual search and navigation • Inference capabilities – Providing information • Methods and tools accounting for the diversity of information sources Semantic Web Portal 9

Introduction to XML-Based Ontology Proof Logic Rules Ontology Sig RDF Schema RDF M&S XML Schema XML URI Semantic Web Portal Namespaces Unicode 10

What is XML? • • Extensible Markup Language A Syntax for Documents A Meta-Markup Language A Structural and Semantic Language, not a Formatting Language • Not just for Web pages Semantic Web Portal 11

Namespace Bindings • Prefixes are bound to namespace URIs by attaching an xmlns: prefix attribute to the prefixed element or one of its ancestors, prefix: name 1 , . . . , prefix: namen • The value of the xmlns: prefix attribute is a URI, which may or (unlike for DTDs!) may not point to a description of the namespace’s syntax • An element can use bindings for multiple name-spaces via attributes xmlns: prefix 1 , . . . , xmlns: prefixm Semantic Web Portal 12

XML Document Instance and DTD <mail: address xmlns: mail="http: //www. deutschepost. de/" xmlns: tele="http: //www. telekom. de/"> <mail: name>Xaver M. Linde</mail: name> <mail: street>Wikingerufer 7</mail: street> <mail: town>10555 Berlin</mail: town> <mail: bill>12. 50</mail: bill> <tele: phone>030/1234567</tele: phone> <tele: phone>030/1234568</tele: phone> <tele: fax>030/1234569</tele: fax> <tele: bill>76. 20</tele: bill> <!ELEMENT address (name, street, town, </ mail: address> bill, phone+, fax+, bill)> <!ELEMENT name (#PCDATA)> <!ELEMENT street (#PCDATA)> <!ELEMENT town (#PCDATA)> <!ELEMENT bill (#PCDATA)> <!ELEMENT phone (#PCDATA)> <!ELEMENT fax (#PCDATA)> 13 Semantic Web Portal <!ELEMENT ARTIST (#PCDATA)>

XML Schema • An XML syntax that's an alternative and/or supplement to DTDs • Data typing of element and attribute content Semantic Web Portal 14

RDF M&S • RDF (Resource Description Framework) – Beyond Machine readable to Machine understandable • RDF consists of two parts – RDF Model (a set of triples) – RDF Syntax (different XML serialization syntaxes) • RDF Schema for definition of Vocabularies (simple Ontologies) for RDF (and in RDF) Semantic Web Portal 15

RDF Data Model • Resources – A resource is a thing you talk about (can reference) – Resources have URI’s – RDF definitions are themselves Resources (linkage, see requirement 1) • Properties – slots, define relationships to other resources or atomic values • Statements – “Resource has Property with Value” – (Values can be resources or atomic XML data) • Similar to Frame Systems Semantic Web Portal 16

A Simple Example • Statement – “Ora Lassila is the creator of the resource http: //www. w 3. org/Home/Lassila” • Structure – Resource – Property – Value (subject) http: //www. w 3. org/Home/Lassila (predicate) http: //www. schema. org/#Creator (object) "Ora Lassila” • Directed graph s: Creator http: //www. w 3. org/Home/Lassila Semantic Web Portal Ora Lassila 17

Another Example • To add properties to Creator, point through an intermediate Resource. http: //www. w 3. org/Home/Lassila s: Creator Person: //fi/654645635 Name Ora Lassila Semantic Web Portal Email lassila@w 3. org 18

Example: Bag • The students in course 6. 001 are Amy, Tim, John, Mary, and Sue /courses/6. 001 Rdf: Bag rdf: type students /Students/Amy rdf: _1 rdf: _2 bagid 1 /Students/Tim rdf: _3 /Students/John rdf: _4 rdf: _5 /Students/Mary /Students/Sue Semantic Web Portal 19

Example: Alternative • The source code for X 11 may be found at ftp. x. org, ftp. cs. purdue. edu, or ftp. eu. net http: //x. org/package/X 11 rdf: Alt rdf: type source altid rdf: _1 ftp. x. org rdf: _2 ftp. cs. purdue. edu rdf: _3 ftp. eu. net Semantic Web Portal 20

RDF Syntax I • Data model does not enforce particular syntax • Specification suggests many different syntaxes based on XML • General form: Starts an RDF-Description Subject (OID) <rdf: RDF> <rdf: Description about="http: //www. w 3. org/Home/Lassila"> <s: Creator>Ora Lassila</s: Creator> <s: created. With rdf: resource=“http: //www. w 3 c. org/amaya”/> </rdf: Description> </rdf: RDF> Literal Properties Resource (possibly another RDF-description) Semantic Web Portal 21

Resulting Graph http: //www. w 3. org/Home/Lassila s: created. With s: Creator http: //www. w 3 c. org/amaya Ora Lassila <rdf: RDF> <rdf: Description about="http: //www. w 3. org/Home/Lassila"> <s: Creator>Ora Lassila</s: Creator> <s: created. With rdf: resource=“http: //www. w 3 c. org/amaya”/> </rdf: Description> </rdf: RDF> Semantic Web Portal 22

RDF Syntax II: Syntactic Varieties Typing Information Subject (OID) In-Element Property <s: Homepage rdf: about="http: //www. w 3. org/Home/Lassila” s: Creator=“Ora Lassila”/> <s: created. With> <s: HTMLEditor rdf: about=“http: //www. w 3 c. org/amaya”/> </s: created. With> </s: Homepage> Property rdf: type s: Homepage http: //www. w 3. org/Home/Lassila s: Creator s: created. With rdf: type Ora Lassila http: //www. w 3 c. org/amaya Semantic Web Portal HTMLEditor 23

RDF Schema (RDFS) • RDF just defines the data model • Need for definition of vocabularies for the data model - an Ontology Language! • The RDF Schema mechanism provides a basic type system for use in RDF models. • The RDF schema specification language is less expressive, but much simpler to implement, than full predicate calculus languages such as Cyc. L and KIF. Semantic Web Portal 24

Most Important Modeling Primitives • Core Classes – Root-Class rdfs: Resource – Meta. Class rdfs: Class – Literals rdfs: Literal • rdfs: subclass. Of-property • Inherited from RDF: properties (slots) • rdfs: domain & rdfs: range • rdfs: label, rdfs: comment, etc. • Inherited from RDF: Instance. Of (rdf: type) Semantic Web Portal 25

DAML+OIL: an Ontology Language • Extension of RDF Schema • Ontology Language DAML+OIL: Result of a Joint (European + US-American) Committee • Extension of RDF Schema – – Class Expressions (Intersection, Union, Complement) XML Schema Datatypes Enumerations Property Restrictions • Cardinality Constraints • Value Restrictions Semantic Web Portal 26

Example: Intersection & Synonyms <daml: Class rdf: ID="Tall. Man"> <daml: intersection. Of rdf: parse. Type="daml: collection"> <daml: Class rdf: about="#Tall. Thing"/> <daml: Class rdf: about="#Man"/> </daml: intersection. Of> </daml: Class> <daml: Class rdf: ID="Human. Being"> <daml: same. Class. As rdf: resource="#Person"/> </daml: Class> Semantic Web Portal 27

Example: Disjoint & Complement <daml: Disjoint rdf: parse. Type="daml: collection"> <daml: Class rdf: about="#Car"/> <daml: Class rdf: about="#Person"/> <daml: Class rdf: about="#Plant"/> </daml: Disjoint> Disjoint not strictly necessary, since expressible via pairwise sub. Class. Of of complement. Of, as for Car and Person: <daml: Class rdf: ID="Car"> <rdfs: comment>no car is a person</rdfs: comment> <rdfs: sub. Class. Of> <daml: Class> <daml: complement. Of rdf: resource="#Person"/> </daml: Class> </rdfs: sub. Class. Of> </daml: Class> 28 Semantic Web Portal

Example: Properties (Transitive, Inverse, sub. Property, Unique. Property, range, Datatypes) <daml: Transitive. Property rdf: ID="has. Ancestor"/> <daml: Object. Property rdf: ID="has. Child"> <daml: inverse. Of rdf: resource="#has. Parent"/> </daml: Object. Property> <daml: Unique. Property rdf: ID="has. Mother"> <rdfs: sub. Property. Of rdf: resource="#has. Parent"/> <rdfs: range rdf: resource="#Female"/> </daml: Unique. Property> <daml: Datatype. Property rdf: ID="age"> <rdf: type rdf: resource="http: //www. daml. org/2001/03/daml+oil#Unique. Property"/> <rdfs: range rdf: resource="http: //www. w 3. org/. . . /XMLSchema#non. Negative. Integer"/> </daml: Datatype. Property> Semantic Web Portal 29

Using User-defined Datatypes (based on XML Schema) <xsd: simple. Type name="over 17">   <xsd: restriction base="xsd: decimal"> <xsd: min. Inclusive value="18"/> </xsd: restriction> </xsd: simple. Type> <daml: Class rdf: ID="Adult"> <daml: intersection. Of rdf: parse. Type="daml: collection"> <daml: Class rdf: about="#Person"/> <daml: Restriction> <daml: on. Property rdf: resource="#age"/> <daml: has. Class rdf: resource="somefile#over 17"/> </daml: Restriction> </daml: intersection. Of> 30 Semantic Web Portal </daml: Class>

Instances (Individuals) <daml: Class rdf: ID="Person">. . . </daml: Class> <Person rdf: ID="Adam"> <rdfs: label>Adam</rdfs: label> <rdfs: comment>Adam is a person. </rdfs: comment> <age><xsd: integer rdf: value="13"/></age> <shoesize> <xsd: decimal rdf: value="9. 5"/> </shoesize> </Person> Semantic Web Portal 31

Web Services Semantic Web Portal 32

DAML-S • Users and software agents should be able to discover, invoke, compose, and monitor Web resources offering particular services and having particular properties. • As part of the DARPA Agent Markup Language program, we have begun to develop an ontology of services, called DAML-S. Semantic Web Portal 33

Top Level of the Service Ontology Resource provides presents Service. Profile (what it does) Service (how to access it) supports (how it works) described by Service Grounding Service. Model Semantic Web Portal 34

Process Modeling Ontology Semantic Web Portal 35

Concept of eb. XML Business Process Specification Schema Semantic Web Portal 36

Business Process Specification in XML Semantic Web Portal 37

KA 2 An Ontology-Based Community Web Portal Semantic Web Portal

KA 2 • Knowledge Annotation Initiative of the Knowledge Acquisition Community • The basic scenario – WWW documents of the KS community were annotated according to the schema of an ontology. – The annotations enable intelligent access to these documents and infer implicit knowledge from explicitly stated facts and rules from the ontology. Semantic Web Portal 39

The KA 2 Ontology Person-ontology Class hierarchy Person Employee Academic-Staff Lecturer Researcher Administrative-Staff Secretary Technical-Staff Student Phd-Student Publication-ontology Class hierarchy On-Line-Publication Article-In-Book Conference-Paper Journal-Article Technical-Report Workshop-Paper Book Journal IEEE-Expert IJHCS Special-Issue Relations Address, Affiliation, Cooperates-With, Editor-Of, Email, First-Name, Has. Publication, Head-Of-Group, Head-Of. Relations Project, Last-Name, Member-Of. Abstract, Book-Editor, Conference. Organization, Member-Of-Program. Proceedings-Title, Contains-Article-In. Committee, Member-Of-Research-Group, Book, Contains-Article-In-Journal, Middle-Initial, Organizer-Of-Chair-Of, Describes-Project, First-Page, Has. Person-Name, Photo, Research-Interest, Author, Has-Publisher, In-Book, In. Secretary-Of, Studies-At, Supervises, Conference, In-Journal, In. Supervisor, Works-At-Project Organization, In-Workshop, Journal-Editor, Journal 40 Semantic Web Portal Number, Journal-Publisher, Journal. Year, Last-Page, On-Line-Version, …

Accessing the Community Web Portal • Query capability – In F-Logic mechanism • Navigating capability – As the easy-to-use front-end of the query mechanism Semantic Web Portal 41

Query Capabilities For all publications of the researcher “Steffen Staab”. FORALL Pub <EXISTS Res. ID: Researcher[NAME->> Steffen "Staab"; PUBLICATION ->> Pub]. Two researchers cooperate, if a Researcher X works at a Project Proj and if a Researcher Y works at the same Project Proj and X is another person than Y FORALL X; Y; Proj X: Researcher[COOPERATESWITH ->> Y: Researcher] <X: Researcher[WORKSATPROJECT->>Proj: Project] AND Y: Researcher[WORKSATPROJECT->>Proj: Project] AND NOT equal(X; Y ): Which researchers are cooperating with other r? FORALL Res. ID 1, Res. ID 2 <Res. ID 1: Researcher[COOPERATESWITH ->> Res. ID 2]. Semantic Web Portal 42

Navigating and Querying the Portal • Query the portal using F-Logic is too inconvenient. • Navigating and querying the web – A hypertext link may contain a query dynamically evaluated when clicking on the link (See P. 45) – Query generated by using the hyperbolic view interface (See P. 46) – Queries may be personalized and for the different users and available for the user in a selection list. – An expert mode: Querying the portal by typing an F-Logic statement Semantic Web Portal 43

Semantic Web Portal 44

Semantic Web Portal 45

Providing Information • Integrating various syntactic and semantic formats based on the common ontology • Three different modes of information provision are supported – Metadata-based information – Wrapper-based information – Fact-based information Semantic Web Portal 46

Metadata-based Information In RDF, XML Metadata Information source Annotation tool (Onto. Pad Annotea, …) Semantic Web Portal 47

Wrapper-based Information • Annotating information sources by hand is timeconsuming. Semi-structured Information sources (e. g. , HTML) Structured Information sources (e. g. , RDB) Wrapper program Metadata (Onto Wrapper) Semantic Web Portal 48

Fact-Based Information New facts Knowledge warehouse create add, modify, delete Fact Editor (Ontoedit, Oil. ED, Protégé 2000) Semantic Web Portal 49

Development of Web Portals Semantic Web Portal 50

The System Architecture Semantic Web Portal 51

An Architecture of RDF Triple Data Store Semantic Web Portal 52

RDF Parser and Generator • Using DCG in Prolog as the development tool • Formal grammar in RDF M&S Spec http: //www. w 3. org/TR/1999/REC-rdf-syntax-19990222/#grammar Formal grammar rules in DCG Prolog’s working storage Prolog’s inference engine Semantic Web Portal User interface 53

[6. 1] RDF [6. 2] obj [6. 3] description [6. 4] container : : = ['<rdf: RDF>'] obj* ['</rdf: RDF>'] : : = description | container : : = '<rdf: Description' id. About. Attr? bag. Id. Attr? prop. Attr* '/>' | '<rdf: Description' id. About. Attr? bag. Id. Attr? prop. Attr* '>' property. Elt* '</rdf: Description>' | typed. Node : : = sequence | bag | alternative rdf(Objs) --> (['<? '], ([nm/'xml']; [nm/'XML']; [nm/'xmls']; [nm/'XMLS']), ([nm/'version', '=', qs/_]; []), ([nm/'encoding', '=', qs/_]; []), ['? >'], {wl('XML heading')} ; []), (full. STG('RDF', NS) ; half. STG('RDF', NS), ['>'] ; [ ]), obj. Star(Objs), (full. ETG('RDF', NS); [ ]). obj. Star(Out) --> obj(O), obj. Star(R), {Out=[O|R]} ; [], {Out=[]}. obj(Obj) --> container(Obj) ; description(_), {get. All. Triples(Obj)}. get. All. Triples(Obj): findall(statement(A, B, C), Obj). description(_) --> half. STG('Description', NS), (id. About. Attr(Id. About. Attr); []), (bag. Id. Attr(Bag. Id. Attr); []), prop. Attr. Star(Id. About. Attr), (['/>'] ; ['>'], property. Elt. Star(Id. About. Attr), full. ETG('Description', NS)), {reification. Of. Statements(Id. About. Attr, B ag. Id. Attr)} ; 54 Semantic Web Portal typed. Node.

<rdf: RDF xmlns: rdf="http: //www. w 3. org/1999/02/22 -rdf-syntax-ns#" xmlns: dc="http: //purl. org/metadata/dublin_core#"> <rdf: Description about="http: //www. foo. com/cool. html"> <dc: Creator> <rdf: Seq ID="Creators. Alphabetical. By. Surname"> <rdf: li>Mary Andrew</rdf: li> <rdf: li>Jacky Crystal</rdf: li> </rdf: Seq> </dc: Creator> <dc: Identifier> <rdf: Bag ID="Mirrored. Sites"> <rdf: li rdf: resource="http: //www. foo. com. au/cool. html"/> <rdf: li rdf: resource="http: //www. foo. com. it/cool. html"/> </rdf: Bag> </dc: Identifier> <dc: Title> <rdf: Alt> <rdf: li xml: lang="en">The Coolest Web Page</rdf: li> <rdf: li xml: lang="it">Il Pagio di Web Fuba</rdf: li> </rdf: Alt> </dc: Title></rdf: Description></rdf: RDF> RDF input [statement(about/http: //www. foo. com/cool. html, Title, alt(_87882, [string/The Coolest Web Page, string/Il Pagio di Web Fuba])), statement(about/http: //www. foo. com/cool. html, Identifier, bag(id/Mirrored. Sites, [resource/http: //www. foo. com. au/cool. html, resource/http: //www. foo. com. it/cool. html])), statement(about/http: //www. foo. com/cool. html, Creator, 55 Semantic Web Portal seq(id/Creators. Alphabetical. By. Surname, [string/Mary Andrew, string/Jacky Crystal]))] Prolog output

RDF Statements in RDB Tables RDF_Name. Space Id 1 2 … Ns. Name http: //www. w 3. org/2000/01/rdf# http: //purl. org/metadata/dublin_core# … RDF_Resource Id 1 2 … Resource. Name http: //www. dlib. org http: //www. foo. com … RDF_Predicate Id 1 2 … NS 2 2 … Predicate. Name Creator Language … RDF_Statement Id 1 2 … Resource 1 1 … Predicate 1 2 … Literal 1 2 … RDF_Literal Id 1 2 … Literal. Name Jacky Crystal English … Semantic Web Portal 56

User Interface Conceptual Search • Natural language interface is the best choice, but is very difficult to obtain a good result. • Form-based interface is easy to implement, but is too restricted. • Hierarchical directory browsing is perhaps a good idea, if the domain in question is well organized. • We also propose a frame-based query interface. target_concept[(attribute 1[: value 1], …)] teacher(office: 6 th_floor) Semantic Web Portal 57

User Interface Natural Language Generation Content extraction Knowledge Warehouse (RDF) Text planning Content planning Multi-sentential text NLG Semantic Web Portal 58

Future Work • Building an ontology for the Digital Archive Services – Consisting of resource and process parts • Declarative approach to semantic web service – Using an workflow engine to interpret the process descriptions • Intelligent Q&A for digital archive Semantic Web Portal 59

Summary • Semantic Web portals – Machine-understandable information – RDF store – Accessing information • Navigation and query – Providing information • Annotation, wrapper, fact editing – Enabling automatic processing by software agents Semantic Web Portal 60