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I V P R 1© Copyright 2003 Haim Levkowitz

Web Services: Introduction and overview

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Outline

• Introduction and overview• Web Services model• Components / protocols …• … In the Web Services model• Web Services protocol stack• Examples

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Introduction and overview• Services offered via the Web• Typical Web services scenario:

• Business application sends request to service at given URL• Using SOAP (protocol) over HTTP

• Service • Receives request• Processes it• Returns response

I V P R 4© Copyright 2003 Haim Levkowitz

Introduction and overview• Common example (simple)

• Stock quote request• Current price of specified stock

• Response: stock price • One of simplest forms of Web service

• Request filled almost immediately• Request and response parts of same

method call

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I V P R 5© Copyright 2003 Haim Levkowitz

Another example• Service: map out efficient route for delivery

of goods• Business sends request

• Containing delivery destinations• Service processes

• Determine most cost-effective delivery route

• Time to return response depends on complexity of routing

• è Response probably sent as operation is separate from request

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Predominantly B-to-B

• Enterprise can be provider & consumer • E.g., wholesale distributor of spices

• Consumer role: check availability of vanilla beans

• Provider role: supply prospective customers different vendors' prices for vanilla beans

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Web application• Dynamic extension of Web server• Two types:

• Presentation-oriented:• Generate dynamic Web pages w/various markup

• HTML, XML, …• Respond to requests

• Service-oriented:• Implement endpoint of Web service• Often invoked by presentation-oriented applications

I V P R 8© Copyright 2003 Haim Levkowitz

Web Services

• Based on XML, lots of Java• Still under development

• Lots of “buzz”• CACM, Oct. 2003• IEEE Computer, Oct. 2003

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Web Services model

Service Provider

Service RegistryService Requestor

Invoke / Bind

Query / Find

Publish

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Components / protocols …• All XML-based• SOAP: Simple Object Access Protocol

• Communication documents• WSDL: Web Service Description Language

• Service description• UDDI: Universal Description, Discovery and

Integration• Service discovery

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InternetInternet

… In the Web Services model

Service Provider

Service Registry & Directory

Service Requestor / Client

3. Invoke / Bind (SOAP + WSDL)

2. Query / Find (UDDI + WSDL )

1. Publish (WSDL)

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Communication (SOAP)

• Exchange documents• In SOAP

• XML

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I V P R 13© Copyright 2003 Haim Levkowitz

Service description (WSDL)

• Tell the outside world:• Interface definition: what kinds of

documents it exchanges• URI – address: where it “lives” • Binding: which transport protocols it can

use to exchange documents• In WSDL

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Service registry & discovery (UDDI)• UDDI deals with registering and discovery of

Web services• UDDI registry is the “yellow pages” to discover

Web services

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I V P R 15© Copyright 2003 Haim Levkowitz

Web Services protocol stack

Transport protocols(HTTP, HTTPS, SMTP, etc.)

XML

SOAP

UDDI

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SOAP

• Communications protocol• Initially created by Microsoft• Provides platform and language

independence

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I V P R 17© Copyright 2003 Haim Levkowitz

SOAP transaction

(from Oracle)

Client SOAP Supplier SOAPTransport

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Structure of SOAP message<SOAP:Envelope xmlns:SOAP=

"http://schemas.xmlsoap.org/soap/envelope/"><SOAP:Header>

<!-- content of header goes here --></SOAP:Header><SOAP:Body>

<!-- content of body goes here --></SOAP:Body>

</SOAP:Envelope> Envelope features child elements that contain message header and body elements

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SOAP message containing an e-ticket

SOAPAction header indicates message’s purpose. In real-world scenario, message would contain additional information, including sender’s credentials

I V P R 20© Copyright 2003 Haim Levkowitz

SOAP RPC call

To find out if flight is on time, Joesends string containing airline’s name and integer with flight number

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I V P R 21© Copyright 2003 Haim Levkowitz

SOAP RPC response

travel service responds to Joe’s request with structured value containing subvalues for gate number + flight status

I V P R 22© Copyright 2003 Haim Levkowitz

WSDL

• XML based• Used to describe and expose Web

Services• Developed by IBM and Microsoft • WSDL document provides Abstract

Description and Concrete Binding Information

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I V P R 23© Copyright 2003 Haim Levkowitz

WSDL doc structure

(from Oracle)

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WSDL – Abstract Description• 3 main components

• Vocabulary• Message• Interaction

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I V P R 25© Copyright 2003 Haim Levkowitz

WSDL –Abstract Description

string and intdata types, def’din XSD, + 2 other datatypesdef’d in external schema:FlightInfoTypeand Ticket, (imported earlier in WSDL file)

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WSDL – Concrete Binding Information• 3 pieces

• What communication protocol:• SOAP over HTTP?

• How to accomplish service interactions• Individual service interactions over this protocol

• Where to terminate communication• The network address

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WSDL –Concrete Binding Information

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I V P R 29© Copyright 2003 Haim Levkowitz

UDDI

• Service discovery• Common repository to advertise• Provides 2 basic specifications

• Organizing structure• Categorization

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UDDI – Organizing Structure• Encodes 3 types of information

• “white pages” (name, addr)• “yellow pages” (categorized)• “green pages” (tech info)

• Organized around two entities• businessEntity• businessService

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SimplifiedbusinessEntitystructure

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SimplifiedbusinessServicestructure

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I V P R 35© Copyright 2003 Haim Levkowitz

UDDI – Categorization

• Taxonomy and tModels• 3 standard taxonomies

• North American Industry Classification System (NAICS)

• Universal Standard Products and Services Code System (UNSPSC)

• International Organization for Standardization Geographic taxonomy (ISO 3166)

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SampletModeldefinition

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Current Web Services Directories• UDDI business registry (UBR)• www.uddi.org• www.xmethods.net (~250)• www.salcentral.com (~540)

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What’s Next?

• Security• SOAP Security Extensions proposal

• Reliability• “Reliable SOAP” standard?

• Quality-of-service (QoS)• Popular = heavy loads

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Summary

• All based XML• All still under development• SOAP + WSDL + UDDI• Security, Reliability, QoS next

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References• Curbera, F.; Duftler, M.; Khalaf, R.; Nagy, W.; Mukhi, N.;

Weerawarana, S., “Unraveling the Web services web: an introduction to SOAP, WSDL, and UDDI”, IEEE Internet Computing Volume: 6, Issue: 2, March-April 2002, pp. 86 -93

• H. M. Deitel et al., Web Services A Technical Introduction (New Jersey, Prentice Hall, 2003)

• S. Short, Building XML Web Services for the Microsoft .NET Platform (Washington, Microsoft Press, 2002)

• Clark, D., Next-generation web services, IEEE Internet Computing Volume: 6, Issue: 2, March-April 2002, pp. 12 -14

• Ingham, D.B.; Shrivastava, S.K.; Panzieri, F., Constructing dependable Web services, IEEE Internet Computing Volume: 4, Issue: 1, Jan.-Feb. 2000, pp. 25 -33.