Web Service is a mechanism by which you can communicate between electronic systems over internet.Web service has the capability to convert an application into a web application which can publish a function or message. Web services constitute a distributed computer architecture made up of many different computers trying to communicate over the network to form one system. They consist of a set of standards that allow developers to implement distributed applications – using radically different tools provided by many different vendors – to create applications that use a combination of software modules called from systems in disparate departments or from other companies.
A Web service contains some number of classes, interfaces, enumerations and structures that provide black box functionality to remote clients. Web services typically define business objects that execute a unit of work (e.g., perform a calculation, read a data source, etc.) for the consumer and wait for the next request. Web service consumer does not necessarily need to be a browser-based client. Console-baed and Windows Forms-based clients can consume a Web service. In each case, the client indirectly interacts with the Web service through an intervening proxy. The proxy looks and feels like the real remote type and exposes the same set of methods. Under the hood, the proxy code really forwards the request to the Web service using standard HTTP or optionally SOAP messages.
Web Service standards
Web services are registered and announced using the following services and protocols. Many of these and other standards are being worked out by the UDDI project, a group of industry leaders that is spearheading the early creation and design efforts.
Universal Description, Discovery, and Integration
(UDDI) is a protocol for describing available Web services components. This standard allows businesses to register with an Internet directory that will help them advertise their services, so companies can find one another and conduct transactions over the Web. This registration and lookup task is done using XML and HTTP(S)-based mechanisms.
Simple Object Access Protocol (SOAP)
is a protocol for initiating conversations with a UDDI Service. SOAP makes object access simple by allowing applications to invoke object methods or functions, residing on remote servers. A SOAP application creates a request block in XML, supplying the data needed by the remote method as well as the location of the remote object itself.
Web Service Description Language (WSDL)
the proposed standard for how a Web service is described, is an XML-based service IDL (Interface Definitition Language) that defines the service interface and its implementation characteristics. WSDL is referenced by UDDI entries and describes the SOAP messages that define a particular Web service.
ebXML (e-business XML)
defines core components, business processes, registry and repository, messaging services, trading partner agreements, and security.
Implementing Web Services
Here comes a brief step-by-step on how a Web service is implemented.
- A service provider creates a Web service
- The service provider uses WSDL to describe the service to a UDDI registry
- The service provider registers the service in a UDDI registry and/or ebXML registry/repository.
- Another service or consumer locates and requests the registered service by querying UDDI and/or ebXML registries.
- The requesting service or user writes an application to bind the registered service using SOAP in the case of UDDI and/or ebXML
- Data and messages are exchanged as XML over HTTP
Web Service Infrastructure
Even though Web services are being built using existing infrastructure, there exists a strong necessity for a number of innovative infrastructures. The core architectural foundation of Web services are XML, XML namespaces, and XML schema. UDDI, SOAP, WSDL, ebXML and security standards are being developed in parallel by different vendors
Web Services Technologies and Tools
There are a number of mechanisms for constructing Web services. Microsoft has come out with a new object-oriented language C# as the development language for Web services and .NET framework. Microsoft has an exciting tool called Visual Studio .NET in this regard. The back end database can be Microsoft SQL Server 2000 in Windows 2000 Professional.
Sun Microsystems has its own set of technologies and tools for facilitating Web services development. Java Servlets, Java Server Pages (JSPs), Enterprise JavaBeans (EJB) architecture and other Java 2 Enterprise Edition (J2EE) technologies play a very critical role in developing Web services.
There are a number of tools for developing Web services. They are Forte Java IDE, Oracle JDeveloper, and WebGain Studio.
Sun Microsystems has taken an initiative called Sun ONE (Open Network Environment) and is planning to push Java forward as a platform for Web services. It is developing Java APIs for XML-based remote procedure calls and for looking up services in XML registries – two more JAX family APIs: JAX/RPC (Java API for XML Remote Procedure Calls) and JAXR (Java API for XML Registries). These will wrap up implementations of Web services standards, such as SOAP and UDDI.
IBM also for its part has already developed a suite of early-access tools for Web services development. They are Web Services Toolkit (WSTK), WSDL Toolkit, and Web Services Development Environment (WSDE).
Apache Axis is an implementation of the SOAP (“Simple Object Access Protocol”) submission to W3C.
From the draft W3C specification:
SOAP is a lightweight protocol for exchanging structured information in a decentralized, distributed environment. It is an XML based protocol that consists of three parts: an envelope that defines a framework for describing what is in a message and how to process it, a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing remote procedure calls and responses.
ApacheAxis is an OpenSourceSOAPserver and client. SOAP is a mechanism for inter-application communication between systems written in arbitrary languages, across the Internet. SOAP usually exchanges messages over HTTP: the client POSTs a SOAP request, and receives either an HTTP success code and a SOAP response or an HTTP error code. Open Source means that you get the source, but that there is no formal support organization to help you when things go wrong.