Web Service is a popular concept in Information technology (IT). A web service is typically an application programming interface (API) or Web API that is accessed via Hypertext Transfer Protocol (HTTP) and executed on a remote system, hosting the requested service.

The web services fall into two kinds. One is called “big web service”, the other is called “Restful web service”. The main difference between them are: big web service use the soap as the protocol when doing the data transmission. Restful web service uses the basic http method, such as ‘get’, ‘post’, ‘put’, etc, to communication between server and client. SOAP protocol is over the http, so it is heavier than restful web service.

The restful web services is specially hot in these year, many applications originally based on the soap, were announced that they were transited to restful web services.

The web service is so hot that many applications were developed as web service to go with the fashion. But actually some of them are not necessary to developed as web service.
The web service have the advantage on the integration different applications and the re-usage of data. The former one is that when there are several applications based on different platforms, and want to integrated them as a whole application. The web service can do well on it, since it is based on the http. The latter one is about that the web service can work well on the heterogeneous data exchange, which provides the common data structure for different data but presenting the same type of data.

But except the above applications, we can use other technology, such as DCom, java RPC. These technologies are lighter than SOAP.

References: Web service from Wikipedia