Hi!
If you have already chosen RESTstyle web service, then one of the few things remaining to decide on is the format of the representation generated by the service.
XML and/or JSON.
In order to be able to decide, I would examine whether the client platform and server platform (for instance
Java or .NET) have some suitable library for efficient marshalling and unmarshalling of the representation format you prefer.
If the server is to be implemented in Java, then a question is whether you want to deploy it as a standalone application or in a web container like
Tomcat?
I would implement a standalone Java server using the Restlet framework. For a service that is to be deployed in a container, I would choose some framework that implements JAX-RS.
Best wishes!