Web Services are the key point of Integration for different applications belonging to different Platforms, Languages, systems. It wouldn’t be wrong if you call Web-services as the “Rendezvous point of the Business”.
•SOAP refers to Simple Object Access Protocol
•HTTP based APIs refer to APIs that are exposed as one or more HTTP URIs and typical responses are in XML / JSON. Response schemas are custom per object
•REST on the other hand adds an element of using standrdized URIs, and also giving importance to the HTTP verb used (ie GET / POST / PUT etc)
Although, in alst ffew years we saw growth of large no. of Web Services, despite that the hype surrounding the SOAP has barely reduced. Internet architects have come up with a surprisingly good argument for pushing SOAP aside: there’s a better method for building Web services in the form of Representational State Transfer (REST).
REST is more of an old philosophy than a new technology. But a realization that came later in technology. Whereas SOAP looks to jump-start the next phase of Internet development with a host of new specifications, the REST philosophy espouses that the existing principles and protocols of the Web are enough to create robust Web services. This means that developers who understand HTTP and XML can start building Web services right away, without needing any toolkits beyond what they normally use for Internet application development.
read more at REST vs. SOAP using HTTP – Choosing the Right WebService Protocol