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G52IWS: Web Services

Chris Greenhalgh

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Contents

The World Wide Web Web Services example scenario Motivations Basic Operational Model Supporting standards Challenges Summary

See “Developing Java Web Services”, chapter 2

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The World Wide Web

Web server

User

Web server

GET/POST request

Document(usually HTML)

Browser

communication:HTTP over TCP/IP

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Example Web Service scenario:arranging a business trip

Service requestor

Travelservicesregistry

Travelreservation

servicesprovider

Airlinereservation

System

HotelReservation

system

Credit cardpaymentsystem

Find services

Invoke services

Register services

Wireless device

Desktop

After “Developing Java Web Services” Figure 2.1

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Scenario notes

Travel reservation service provider exposes travel services via web service interfaces

These are registered with (described in) the travel services registry

A customer discovers the service(s) from the registry (or other search engine)

They then directly request things (“services”, e.g. a reservation) from those web services

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Definitions

“Web services are loosely coupled software components delivered over Internet standard technologies” Gartner research, June 15 2001

Informally: web services are like web sites but... Providing access to all kinds of services, not just

documents For computers rather than people to use

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Motivations

Based on XML messaging Loosely coupled – abstracted service interfaces Use any common programming language Industry standard protocols (HTTP)

Familiar and simple Internet scope Firewall compatibility Established mechanisms for scalability, robustness,

etc.

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Motivations cont.

Usable by many types of client Support a range of levels of functionality from

trivial to profound Supported by other middleware/platforms

e.g. J2EE, CORBA, Microsoft .NET Support dynamically locatable and invocable

services Support cross-platform integration of business

applications over the internet

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Basic Operational Model of Web Services

Service Broker

Service Provider

Service Requestor

DiscoverService

Invoke service

Register service

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Core Web Service Standards

Extensible Markup Language (XML) How to encode arbitrary information in document

form Simple [Standard] Object Access Protocol

(SOAP) How to express web service requests and

responses in XML Web Services Definition Language (WSDL)

Defines the operations, data types and faults that characterise a web service

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Core Web Service Standards (cont.)

Universal Description, Discovery and Integration (UDDI) How to describe, publish, store and retrieve

information about web services in registries WS-Security

Various security-related facilities & definitions, including XML Encryption, XML Key Management System, XML Signature, ...

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Supporting standards

TCP/IP The Internet Protocol suite for reliable global

communication DNS – the Domain Name System

The standard Internet naming protocol HyperText Transfer Protocol (HTTP)

A common “binding” for SOAP – to carry SOAP requests and responses

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Basic Operational Model of Web Services w. standards

Service Broker

Service Provider

Service Requestor

DiscoverService

Invoke service

Register service

Communication:typically SOAP (XML) over HTTP over TCP/IP

Optionally secured using WS-Security

Interface definition:WSDL (esp. for dynamic invocation)

Registry:UDDI & WSDL

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Other related standards

ebXML Complementary standards specific to e-business

Web Services Choreography Interface Standard(s) for defining more complex patterns of

interaction between web services Business Transaction Protocol

Support for web service distributed transactions

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Challenges for web services

Distributed transactions Coordinated success, failure and recovery

Quality of Server (QoS) Reliability and dependability. Service-level agreements

Security Publicly exposed core business services and

operations!

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Summary

Like a WWW for computers Publishing “services” rather than documents In XML (for machines) rather than HTML (for

people) Using standard technologies (XML, HTTP, ...)

Especially for Business-to-business integration and

interoperability Other loosely-coupled distributed applications

e.g. bioinformatics