What is Web Service in ASP.net?
A web service is a special kind of web site. It is different from a traditional ASP.NET web site that produces HTML code. In fact, a web service had no graphical user interface and produces XML. A web service exposes one or more methods that your application can call remotely. This is called a remote procedure call. It basically means that you can have web service A sitting on a web server and another ASP.NET web application B sitting on a different server, and application B can call or communicate with web service A, even though they are in separate physical machines.
It turns out that this feature of web services makes them very useful for many reasons: scalability, encapsulation of logic, and security.
Web services are implemented internally using an Internet protocol called SOAP, which passes XML messages back and forth between a web service client application and a web service. The SOAP protocol is an Internet standard which makes web services interoperable or cross-platform (e.g. Java can communicate with .NET and .NET can communicate with Java); the two can integrate with each other seamlessly by using web services. You don’t have to understand how SOAP works in order to program an ASP.NET web service, and a lot of programmers probably don’t. That is one of the strengths of the .NET framework and the Visual Studio IDE.