THE CONCEPT OF A WEB SERVICE HAS ALREADY BEEN INTRODUCED IN THE WEB SERVICE PATTERN, BUT the pattern leaves open many questionsfor instance, what sort of messages will be sent to and from the service? How will the URLs look? How will the service relate to backend software? These are the kind of design and programming issues covered in this chapter.
RESTful Service is an overview of Representational State Transfer (REST), a popular set of patterns and idioms for consistent and intuitive web services. RPC Service has similar goals, but with a philosophy that leads to very different services. Neither REST nor Remote Procedural Call (RPC) are Ajax-specific, because they are general industry conventions for web services. However, the next pattern, Ajax Stub, is Ajax-specific, because it provides a convenient way to invoke RPC-style services from the browser.
The remaining patterns look at popular message formats used for communication between the browser and Web Services. HTML Message is a message in HTML form, usually sent from the server to be morphed directly onto the page. In contrast, the remaining messages are raw responses that usually can't be displayed directly, and that may be transferred in both directions. They are Plain-Text Message, XML Message, and JSON Message.