XML Web Services are .Net components , which reply to Http requests using the SOAP protocol (Simple Object Access Protocol). XML is one of the principal cornerstones of .Net technology which enables a high degree of interoperability between applications using the Internet. XML Web services are ASP.Net applications which handle requests for .asmx files.

The .asmx extension signals to ASL.Net that it contains non-visual components which are using the XML protocol. These files have a WebService header line which declares it as an XML WebService class. And each method has a WebMethod attribute to make the procedure accessible through the Internet.