A mobile app interfaces with your business logic and data store via an API provided by the application server middle-tier. Exactly how this API is implemented and how the client uses it is up to the developers of the system. In the past, this has often meant using web services (over HTTP) with information interchange via Simple Object Access Protocol (SOAP).
Recently, RESTful APIs have become the norm when working with web and mobile applications. These APIs conform to the following constraints: