Methods of a class that implement a Web service do not automatically have the ability to receive Web service requests and send back responses, but with Web services created using ASP.NET, it is very simple to add that capability. Apply a WebMethod attribute to public methods. Methods of a Web service class that can be communicated with over the Web are called Web service methods.
Web service methods are a key part of the messaging infrastructure employed by Web services. That is, a client and a Web service communicate using messages, specifically SOAP messages, by default. Clients send a SOAP request to a Web service and a Web service method typically returns a SOAP response. Web services define the type of messages they accept using operations, as defined by Web Services Description Language (WSDL). These operations correlate to each of the Web service methods within a Web service.
Even though each of these Web service methods are defined in ASP.NET using a method of a class, it is important to realize that the data that is eventually communicated over the network must be serialized into XML. As such, it is important to remember that Web services are not a replacement for DCOM, but rather a messaging infrastructure for communicating across platforms using industry standards.