Web Services

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Distributed Information Systems Distributed Information Systems 20042004 Web ServicesWeb Services -- -- 11

Web Services

Yih-Kuen Tsay

Dept. of Information Management

National Taiwan University

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What Are Web Services?

• Modular applications accessible by standard protocols over the Internet

• Interfaces described by XML-based WSDL (Web Service Description Language)

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General Process of Engaging a Web Service

Source: www.w3.org

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Characteristics of Web Services

• Semantically encapsulated discrete functionality

• Loosely coupled, reusable components

• Programmatically accessible

• Distributed over the Internet

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Web Services Architecture Stack

Source: www.w3.org

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The Core Layers

• Common Internet Protocols (HTTP, HTTPS, SMTP, …): the basic communication framework for Web services

• XML: a widely accepted format for exchanging data and its corresponding semantics

• SOAP: an XML-based protocol for messaging and RPC-style communication between applications (in a distributed environment)

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• WSDL: an XML-based description of how to connect to a particular Web service

• UDDI: a set of protocols and a public directory for registration and real-time lookup of Web services

• BPEL4WS: a framework for defining new business processes that utilize existing web services.

* ebXML: defines core components, business processes, registry and repository, messaging services, ...

The Higher-Level Layers

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Distributed Information Systems Distributed Information Systems 20042004 Web ServicesWeb Services -- -- 88Source: Sun Microsystems, Inc.

Implementation Models of Web Services

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UDDI Registries

• White pages: information about a service provider– business name, text description, contact information, ...

• Yellow pages: business categories– NAICS, UN/SPSC, Geographical Information, …

• Green pages: information that describes how to work with someone– business processes, service descriptions, binding

information, …

Source: www-3.ibm.com

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Source: Sun Microsystems, Inc.

Core Structures of UDDI

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TModels in UDDI• Categories & Identifiers

– Categorization and identification taxonomies are tModels

– Categories and identifiers are tModel Instances

• WSDL Port Types and Services– WSDL port types are tModels– WSDL services that are bound to a port type

are tModel instances

* TModels represent the extent of UDDI’s semantic description capabilities.

Source: adapted from “www.semanticweb.org/SWWS/program/jamessnell.ppt”

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How WSDL Works

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Discovery Process

Source: www.w3.org

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A Service Brokering Architecture

Customer/Agent

WebServices

Registries

Web Service

Web Service

Web Service

Execution Engine

Ontologies

InferenceCache

InferenceModule

Inference EngineService Composer Service Annotator/Collector

ServiceDescriptions,

Provider/Service ProfilesInference

Module

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• JAXR (Java API for XML Registries): to look up the business partner's web service.

• JAX/RPC (Java API for XML RPC): to send RPC requests to external web services.

• JAXM (Java API for XML Messaging): to send SOAP/ebXML messages to external web service.

• JAXP (Java API for XML Parsing) and JAXB (Java API for XML Binding): to transform Java data into an XML format and to convert the received XML data back into a Java language construct, and to perform XSLT transforms to convert schemas.

The JAX* Suite

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Simple Object Access Protocol(SOAP)

• For information exchange in a distributed environment

• Message format based on XML

• Can be combined with various transport protocols

• Originally developed by Microsoft

• SOAP Version 1.2 now a W3C recommendaton

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Parts of SOAP

• The SOAP envelope: for describing what is in a message and how to process it.

• The SOAP binding framework (added in Version 1.2): for exchanging SOAP envelopes between peers using an underlying transport protocol

• The SOAP encoding rules: for exchanging instances of application-defined data types.

• The SOAP RPC representation: a convention for representing remote procedure calls and responses.

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<env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope"> <env:Header> <n:alertcontrol xmlns:n="http://example.org/alertcontrol"> <n:priority>1</n:priority> <n:expires>2001-06-22T14:00:00-05:00</n:expires> </n:alertcontrol> </env:Header> <env:Body> <m:alert xmlns:m="http://example.org/alert"> <m:msg>Pick up Mary at school at 2pm</m:msg> </m:alert> </env:Body></env:Envelope>

A SOAP Message

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Source: http://www.w3.org/TR/soap12-part1/

Composition of a SOAP Envelope

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<env: Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope/" env:encodingStyle="http://www.w3.org/2001/09/soap-encoding/"> <env:Header> <t:Transaction xmlns:t="some-URI"> env:mustUnderstand="1" 5 </t:Transaction> </env:Header> <env:Body> <m:GetLastTradePrice xmlns:m="some-URI"> <symbol>DEF</Symbol> </m: GetLastTradePrice> </env:Body></env : Envelope>

A SOAP Envelope

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• Request (partial)<env:Body>

<m:GetLastTradePrice xmlns:m="some-URI"> <symbol>DEF</symbol> </m:GetLastTradePrice>

</env:Body>

• Response (partial)<env:Body>

<m:GetLastTradePriceResponse xmlns:m="some-URI"> <price>22.50</price> </m: GetLastTradePriceResponse>

</env:Body>

SOAP Request and Response

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POST /StockQuote HTTP/1.1Host: www.example.orgContent-Type: text/xml; charset="utf-8"Content-Length: nnnnSOAPAction: "http://example.org/2001/06/quotes"

<env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope" > <env:Body> <m:GetLastTradePrice env:encodingStyle="http://www.w3.org/2001/09/soap-encoding" xmlns:m="http://example.org/2001/06/quotes"> <symbol>DIS</symbol> </m:GetLastTradePrice> </env:Body></env:Envelope>

SOAP Message in an HTTP Request

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POST /StockQuote HTTP/1.1HTTP/1.1 200 OKContent-Type: text/xml; charset="utf-8"Content-Length: nnnn

<env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope" > <env:Body> <m:GetLastTradePriceResponse env:encodingStyle="http://www.w3.org/2001/09/soap-encoding" xmlns:m="http://example.org/2001/06/quotes"> <Price>34.5</Price> </m:GetLastTradePriceResponse> </env:Body></env:Envelope>

SOAP Message in an HTTP Response

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A SOAP Use Case

Documents

Web Services