Web Service: Roles

•Service Provider:
•Provides a service component
•Publishes the interface to the broker (UDDI)
•Service Requestor:
•Discover a service from a Service Broker
•Invoke (RPC) the service from the Service Provider. (Using Endpoint)
•Service Broker:
•Register available services from Service Providers
•Make matches with requests from Service Requesters.

Technologies that are needed to implement/use a Webservice

•XML
•A text-based markup language used for the definition of portable structured data.
•SOAP
•Simple Object Access Protocol is an XML-based protocol for the exchange of information in a distributed environment. (XML over HTTP). SOAP is a specification given by W3C
•Service always expects a SOAP request
•Service always sends a SOAP response to the client.
•AXIS
•Apache Axis is an implementation of the SOAP
•WSDL
•WSDL or Web Services Description Language is an XML format for describing network services as a set of endpoints operating on messages, these messages are described abstractly, and then bound to a concrete network protocol and message format to define an endpoint.
•UDDI
•The Universal Description, Discovery, and Integration specification provides a common set of SOAP APIs that are used to register the service to the UDDI registry.

What are the essential activities need to happen in any service-oriented environment

•Web service needs to be created, and its interfaces and invocation methods must be defined.
•Web service needs to be published to one or more intranet or Internet repositories.
•Web service needs to be located to be invoked by potential users.
•Web service needs to be invoked to be of any benefit.
•Web service may need to be unpublished when it is no longer available or needed.

Why do we need a Web Service?

Software applications written in various programming languages and running on various platforms can use web services to exchange data over computer networks like the Internet in a manner similar to inter-process communication on a single computer.

Web Service is:
•A collection of one or more functions/methods/software resources.
•Packaged as a single entity (encapsulate implementation details).
•Published on the network.
•Available for use by other programs, users and web services over the network.
Examples:
•Microsoft Passport authentication service.
•Stock Quote service.
•Credit checking service to obtain a persons credit information

What is a Web Service?

A Web service is defined by the W3C as "a software system designed to support interoperable Machine to Machine interaction over a network." Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.

(OR)

Web Services are self-contained, modular applications that can be described, published, located, and invoked over a network, generally, the Web.