ไปเจอมาจาก Creating and Consuming Web Services With PHP
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we will compare and contrast three methods of consuming and producing web services: XML-RPC, SOAP and REST
Remote Procedure Calls are used to establish and facilitate transactions between two remote systems. Example of popular RPC implementations include DCOM and CORBA. XML-RPC is an established implementation of RPC that allows you to transport XML encoded data between two servers using HTTP.
SOAP is designed as an XML wrapper for web services requests and responses. SOAP's strength lies in its use of namespaces, XML Schema datatypes, and its flexibility with regard to transports. The disadvantage of SOAP is the fact that the specs and implementation is more complex, especially when you compare it to the simple XML-RPC approach. SOAP is the bread and butter of corporate web service developers. It has been deeply integrated into Microsoft .NET and IBM WebSphere. Based on its popularity, Google and Amazon.com have both created SOAP-based Web services.
REST (Representational State Transfer)
REST differs a great deal from SOAP and XML-RPC. First, it's not a standard, whether formal or informal. Second, there is no standardized toolkit or pre-built client and server classes in PHP. The strength of REST is that you won't need special extensions or tools to develop web services. The HTTP protocol specifications contains everything you would need to transmit and receive XML messages.
REST, which stands for "Representational State Transfer", is a simpler approach than XML-RPC or SOAP, using standard HTTP methods such as GET, POST and PUT to send and retrieve XML data. You can then use tools like PHP DOM, SAX, or even XSL to do the parsing. The downside is that everything has to be built by hand (though REST toolkits and frameworks are starting to appear in some languages). If you want to develop REST web services, you must thoroughly understand XML and HTTP. Expect to have to write a little more code yourself.