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Chapter 7. Technology options 129

򐂰 Standardization: When multiple applications use XML to communicate with

each other they need to agree on the tag names they are using. While

industry-specific standard tag definitions often do exist, you can still declare

your own non-standard tags.

򐂰 Large size: XML documents tend to be larger in size than other forms of data

representation.

7.3 Web services

The W3C’s Web Services Architecture Working Group has jointly come to

agreement on the following working definition of a Web service:

“A Web service is a software application identified by a URI, whose interfaces

and bindings are capable of being defined, described, and discovered as

XML artifacts. A Web service supports direct interactions with other software

agents using XML-based messages exchanged via Internet-based protocols.”

Basic Web services combine the power of two ubiquitous technologies: XML, the

universal data description language, and the HTTP transport protocol widely

supported by browser and Web servers.

Web services = XML + transport protocol (such as HTTP)

Some of the key features of Web services are as follows:

򐂰 Web services are self-contained.

On the client side, no additional software is required. A programming

language with XML and HTTP client support, for example, is enough to get

you started.

On the server side, merely a Web server and a servlet engine are required. It

is possible to Web service enable an existing application without writing a

single line of code.

򐂰 Web services are self-describing.

Neither the client nor the server knows or cares about anything besides the

format and content of request and response messages (loosely coupled

application integration).

The definition of the message format travels with the message. No external

metadata repositories or code generation tools are required.

򐂰 Web services are modular.

Web services are a technology for deploying and providing access to

business functions over the Web; J2EE, CORBA, and other standards are

technologies for implementing these Web services.

130 Broker Interactions for Intra- and Inter-enterprise

򐂰 Web services can be published, located, and invoked across the Web.

The standards required to do so are:

– Simple Object Access Protocol (SOAP), also known as service-oriented

architecture protocol, an XML-based RPC and messaging protocol

– Web Service Description Language (WSDL), a descriptive interface and

protocol binding language

– Universal Description, Discovery, and Integration (UDDI), a registry

mechanism that can be used to look up Web service descriptions

򐂰 Web services are language independent and interoperable.

The interaction between a service provider and a service requester is

designed to be completely platform and language independent. This

interaction requires a WSDL document to define the interface and describe

the service, along with a network protocol (usually HTTP).

Because the service provider and the service requester have no idea what

platforms or languages the other is using, interoperability is a given.

򐂰 Web services are inherently open and standards-based.

XML and HTTP are the technical foundation for Web services. A large part of

the Web service technology has been built using open source projects.

Therefore, vendor independence and interoperability are realistic goals.

򐂰 Web services are dynamic.

Dynamic e-business can become a reality using Web services because, with

UDDI and WSDL, the Web service description and discovery can be

automated.

򐂰 Web services are composable.

Simple Web services can be aggregated to more complex ones, either using

workflow techniques or by calling lower-layer Web services from a Web

service implementation.

WebSphere V5.0 provides support for Web services. WebSphere applications

can send and receive SOAP messages and also communicate with UDDI

registries to publish and find services.

For detailed information on Web services, check out the following sources:

򐂰 The IBM Redbook:

WebSphere Version 5 Web Services Handbook, SG24-6891

򐂰 The World Wide Web Consortium (W3C) Web site at:

http://www.w3.org/