Programming Tutorials

Web services basics

By: Saravanan D. Rao  

Web services technologies provide a language-neutral, environment-neutral programming model that accelerates application integration inside and outside the enterprise. 

A Web service is an interface that describes a collection of operations that are network-accessible through standardized XML messaging. 

A Web service performs a specific task or a set of tasks and services and is described using a standard, formal XML notation, called its service description, which provides all of the details necessary to interact with the service, including message formats (that detail the operations), transport protocols, and location.  Web service descriptions are expressed in WSDL. 

Advantages of web services

• Interoperability among distributed applications that 
  span diverse hardware and software platforms
• Easy, widespread access to applications through 
  firewalls using Web protocols 
• A cross-platform, cross-language data model (XML) 
  that facilitates developing heterogeneous distributed
  applications
• Use of Standard protocols and specification enables 
  integration with Other Messaging Systems, Legacy 
  Systems, etc
• Seamless Integration of B2B applications

Web Service Components

1. SOAP – Message Protocol
SOAP provides a simple and lightweight mechanism for exchanging structured and typed information between peers in a decentralized, distributed environment using XML 

2. WSDL – Service Description
Web Services Description Language (WSDL) is an XML format for describing Web services. WSDL enables one to separate the description of the abstract functionality offered by a service from concrete details of a service description such as "how" and "where" that functionality is offered.

3. UDDI – Service Registry
The Universal Description, Discovery and Integration (UDDI) specification defines a standard way to describe a Web service; register a Web service in a well-known registry; and discover other registered Web services. 

Technologies Used in J2EE

1. JAX-RPC

The Java API for XML-based RPC (JAX-RPC) is a Sun Microsystems specification that defines the client API for invoking a Web service

2. JAXR

The Java API for XML-Registries defines how to publish a Web service in a registry such as a UDDI or ebXML registry, or search a registry for a Web service

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