Introduction

What is a Web Service

A web service is a wrapper around a program that is deployed so that others can use it (i.e. as a service) that is described in XML (The WSDL - Web Services Description Language - dialect) so that it is self-describing.

The fact that it is self-describing allows the automation of its use by workflow creation engines and so on.

Data transfer to/from web services is also in XML via SOAP (Simple Object Access Protocol) messages.

A web service provides a component in a Service Oriented Architecture (SOA).

The Anatomy of an Undeployed Web Service

A web service comprises:

• Its description in WSDL (Web Services Description Language). This will describe what it does, what sort of data you need to send to it and how, and what data you can expect back from it.
• The executable service itself.
  

The Anatomy of a Deployed Web Service

A deployed web service is one that is running on a machine, and is an undeployed one that has gone through a deployment (aka provisioning) step.

• It comprises the description but also a series of endpoints that describe where it is running and how you can talk to it.

• The executable service itself.

Provisioning a Web Service

They are normally deployed into web application engines (Tomcat, Axis, etc).

Creating a Web Service

This is generally not trivial, but there are various tools being worked on (e.g. at York) to allow a command-line application to be quickly turned into a web service.