背景： Amazon等公司把他们按照HTTP URL进行直接调用的API称作 REST形式的Web Service(V.S. SOAP形式的WS)。使得REST似乎与Web Services也扯上了关系。孟岩的一篇博客文章中谈到了他自己对于web集成的未来的看法：REST胜过SOAP。

但REST一词最初出现时的含义却不是这样。曾参与HTTP1.1起草工作的Thomas Fielding 2000年在UC Irvine提交的博士论文中，将REST定义成一种web设计风格，强调可缓存、无状态、统一接口等。 w3c近两年中有人做的PPT中指出：两者并不对立，SOAP也可以按照REST风格来使用。

当然，这些都是产业界的事情，研究界的paper中似乎还很少涉及REST。

附：自己看Fielding的博士论文英文版时所做的笔记。

REST: REpresentational State Transfer  

目标：定义一个model of how the World Wide Web (被看作一种Internet-scale distributed hypermedia system) should work.. 在90s中期提出后，作者把它应用于自己制定HTTP/1.1和URI两个RFC的过程中，以及在libwww-perl, Apache httpd等商业级项目的开发中。

其目标是使得延时最小，而同时能保持 组件 的独立性和可扩展性。描述方式是：应用一组体系结构上的约束（来自于对5种Network-based Architectural Styles的分析）。REST的内容有：

l       强调connector，而不是component，的语义;    即It does constrain the interface between components, and hence the scope of interaction and implementation assumptions that might otherwise be made between components.

l       重视caching, intermediary的作用;   --> layering of transformation，即在C/S结构中使用cache，proxy等

l       使用合适的资源表示方式;    <-- REST components perform actions on a resource by using a representation to capture the current or intended state of that resource and transferring that representation between components. A representation is a sequence of bytes, plus representation metadata to describe those bytes. 其它一些不大准确的名称有：document, file, and HTTP message entity, instance, or variant.

l       server不维护会话状态，（处理消息时只需要考虑当前请求的URI及消息内容）。

l       REST constrains messages between components to be self-descriptive in order to support intermediate processing of interactions.

所分析的5种Style是：

l         Data-flow Style
l         Replication Style
l         Hierarchical Style
l         Mobile code Style
l         Peer-to-Peer Style

the characteristics of REST（by Roger L. Costello, http://www.xfront.com/REST-Web-Services.html）：
*    Client-Server: a pull-based interaction style: consuming components pull representations.
*    Stateless: each request from client to server must contain all the information necessary to understand the request, and cannot take advantage of any stored context on the server.
*    Cache: to improve network efficiency responses must be capable of being labeled as cacheable or non-cacheable.
*    Uniform interface: all resources are accessed with a generic interface (e.g., HTTP GET, POST, PUT, DELETE).
*    Named resources - the system is comprised of resources which are named using a URL.
*    Interconnected resource representations - the representations of the resources are interconnected using URLs, thereby enabling a client to progress from one state to another.
*    Layered components - intermediaries, such as proxy servers, cache servers, gateways, etc, can be inserted between clients and resources to support performance, security, etc.