The Semantic Web Service

Shuying Wang2004.02

Outline

• Semantic Web vision• Core technologies

• XML, RDF, Ontology, Agent…

• Web services• DAML-S

What is the Semantic Web?

A vision of possibilities

“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 cooperation.”

The goal of Semantic Web

• In the Semantic Web we will need:• Machines talking to machines – semantics need to

be unambiguously declared• Joined-up data – enabling complex tasks based

on information from various sources• Wide scope – from, say, home to government to

commerce• Trust – both in data and who is saying it

• This is not going to be easily achieved

Layers of the Semantic Web

Semantic Web Architecture

Core technologies

• eXtensible Markup Language (XML)

• Resource Description Framework (RDF)

• Ontologies• Software agents

Uniform Resource Identifier (URI)

• A URI with a fragment identifier is taken to denote an object described in the knowledge base identified by the base URI.

• The URI is the foundation of the Web• A URI provides an identifier for a resource• Everyone can create a URI• We use URI to solve the ambiguous name. The

names we use are web addresses

XML (eXtensible Markup Language)

• Standard designed to transmit structured data to Web applications

• Describes structure & content• Provides syntactic interoperability• XML namespaces qualify element

names uniquely on the Web in order to avoid conflicts between elements with the same name

Metadata in XML

A sentence: “I just got a new pet dog.”XML:<sentence

xmlns="http://example.org/xml/documents/"xmlns:c="http://animals.example.net/xmlns/">

<c:person c:href="http://aaronsw.com/">I</c:person> just got a new pet<c:animal>dog</c:animal>.</sentence>

RDF(Resource Description Framework)

RDF--the Resource Description Framework--is a universal format for data on the Web. Using a simple relational model, it allows structured and semi-structured data to be mixed, exported and shared across different applications. Where XML provides interoperability within one application (e.g. bank statements) using a given schema, RDF provides interoperability across applications (eg import your bank statements into your calendar).• interoperability of data machine • understandable semantics for metadata • better precision in resource discovery than full text search • future-proofing applications as schemas evolve

RDF Data Model

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:dc="http://purl.org/dc/elements/1.1/"> <rdf:Description rdf:about="http://doc" dc:creator= "Wang" dc:title=“page.html" dc:description=“Wang's ramblings about his summer vacation.“dc:date=“2004-02-10" /> </rdf:RDF>

Resource ValuePropertyType

Property

RDF Data Model

Wangwritten by

10-Feb-04

on

page.htmlResource has property valuePage.html written-by Wang

Known as triples or tuples

Ontologies

• An ontology formally defines a common set of terms that are used to describe and represent a domain (e.g., librarianship, medicine, etc.)

• Ontologies include computer-usable definitions of basic concepts in the domain and the relationships among them

• Ontologies are usually expressed in a logic-based language

Ontologies

XML DTDs:• Document Type Definition• Define structure: Car application contains a price

(integer), description and colour

XML Schemas:• Allows richer definitions• Define structure: Car application contains a price

(+ve integer between 1 and 20,000), description and colour (taken from fixed vocabulary)

Ontologies:• Define relationships• Builds on AI techniques

Three Levels of generality in a domain ontology

Foundational ontology

Core ontology

SpecificDomainontology

Web Services

The web is organized around URIs, HTML, and HTTP.

• URIs provide defined ids to refer to elements on the web,

• HTML provides a standardized way to describe document structures (allowing browsers to render information for the human reader), and

• HTTP defines a protocol to retrieve information from the web.

Not surprisingly, web services require a similar infrastructure around UDDI, WSDL, and SOAP.

UDDI

HTML

HTTP

URI

WSDL

SOAP

Web Services

• UDDI provides a mechanism for clients to find web services. A UDDI registry is similar to a CORBA trader, or it can be thought of as a DNS service for business applications.

• WSDL defines services as collections of network endpoints or ports. A port is defined by associating a network address with a binding; a collection of ports define a service.

• SOAP is a message layout specification that defines a uniform way of passing XML-encoded data. It also defines a way to bind HTTP as the underlying communication protocol. SOAP is basically a technology to allow for “RPC over the web”.

Semantic Web Services

The Semantic Web services vision is to describe Web services’ capabilities and content in an unambiguous, computer-interpretable language and improve the quality and robustness of existing tasks, such as Web service discovery and invocation.

Semantic Web Services will also enable a broad range of new automation tasks that human previously formed, including automated composition, interoperation, execution monitoring, and recovery.

DAML-S(DARPA Agent Markup Language)

• The Semantic Web Services arm of the DAML program is developing an OWL-based Web Service Ontology, OWL-S (formerly DAML-S), as well as supporting tools and agent technology to enable automation of services on the Semantic Web.

• OWL-S supplies Web service providers with a core set of markup language constructs for describing the properties and capabilities of their Web services in unambiguous, computer-interpretable form. OWL-S markup of Web services will facilitate the automation of Web service tasks including automated Web service discovery, execution, interoperation, composition and execution monitoring.

DAML-S

Service

Service Model

Service Profile

Resources

Service Grounding

provides

presents

Described by

supports

What the service does

How it works

How to access it

Software agents

• “. . .programs that collect Web content from diverse sources, process the information and exchange the results with other programs”

• Software agents will become effective as more well-defined content & other agents become available

Resources

• Semantic Web, W3C<http://www.w3c.org/2001/sw/>

• Semantic Web Road map, Tim Berners-Lee<http://www.w3c.org/DesignIssues/Semantic.html>

• The Semantic Web, Scientific American<http://www.sciam.com/2001/0501issue/0501berners-lee.html>

• The Semantic Web Community Portal, <http://www.semanticweb.org/>

• The Semantic Web: A Primer<http://www.xml.com/pub/a/2000/11/01/semanticweb/>

• DAML<http://www.daml.org>

• All found using Google to search for “semantic Web”