A web service is a distributed application whose components are deployed and executed on distinct devices. Web services are roughly divided on SOAP-based and REST-style. A SOAP-based service delivered over HTTP can be considered as a special case of a REST-style service.
Acronym SOAP has two meanings: Simple Object Access Protocol or Service Oriented Architecture (SOA) Protocol.
Clients of web services are usually an application that doesn't have a graphical user interface. A client of the SOAP web service sends a SOAP document as a request to a web service, which returns another SOAP document as a response. A client of the REST can send a standard HTTP request to a web service and receive as a response an appropriate XML document.
The web services features:
- Open infrastructure.
- Language transparency.
- Modular design.
WS-I (Web Services-Interoperability) helps software architects and developers to create web services which can interoperate seamlessly despite differences in platforms and programming languages.