At level 0, the API uses the implementing protocol (normally HTTP, but it doesn't have to be) like a transport protocol. There is no effort to utilize the protocol to indicate state; it is just used to pass requests and responses back and forth. The system typically has one entry point (URI) and one method (normally POST in the case of HTTP). For the hotels API, this means that the URL would be /hotels and all APIs would be POST to that, with the payload carrying more information about the request type and related data. Examples include SOAP and XML-RPC