A Web service may be defined as an independent and self-sustained unit of a software application that is hosted on the Web and implement specific functionalities to execute the business logic. A Web service provides so many functionalities, such as generating pay slips for employees, computing tax, broadcasting weather report, and providing updated news. The Web service allows application to share information or exchange data with other applications across different operating systems and hardware.

Therefore, the work of a Web service is to unite software by exchanging data irrespective of their operating systems, supported hardware, and programming language used in their development. The Web services transfer data in the XML format and use Simple Object Access Protocol (SOAP) to communicate. It is an XML based protocol. The Web services use Web Services Description Language (WSDL) and Universal Description, Discovery, and Integration (UDDI) to describe itself.

The advantages of Web services over COM and DCOM are as follows:
• Web services are simple to use and can be implemented on varied platforms.
• Web services are loosely coupled; as a result, their interfaces and methods can be extended.
• Web services do not carry any state information with them so that multiple requests can be processed simultaneously.

System.Web.Services is the elementary namespace, which must be imported to develop code of a Web service.

The portType element contains the operations exposed by the Web service, and the messages involved in the communication between the Web service and its consumers.

DISCO is a technology developed by Microsoft to publish and discover Web services. It discovers URLs of all XML Web services located on a Web server and creates a list of these Web services in a file called as a DISCO file.