SOAP 

SOAP was originally an acronym for Simple Object Access Protocol. (Now it’s just a name.) SOAP 1.1 is the standard messaging protocol used by J2EE Web Services, and is the de facto standard for Web services in general. SOAP’s primary application is Application-to-Application (A2A) communication. Specifically, it’s used in Business-to-Business (B2B) and Enterprise Application Integration (EAI), which are two sides of the same coin: Both focus on integrating software applications and sharing data. To be truly effective in B2B and EAI, a protocol must be platform-independent,flexible, and based on standard, ubiquitous technologies. Unlike earlier B2B and EAI technologies, such as CORBA and EDI, SOAP meets these requirements, enjoys widespread use, and has been endorsed by most enterprise software vendors and major standards organizations (W3C, WS-I, OASIS, etc.).Despite all the hoopla, however, SOAP is just another XML markup language accompanied by rules that dictate its use. SOAP has a clear purpose: exchanging data over networks. Specifically, it concerns itself with encapsulating and encoding XML data and defining the rules for transmitting and receiving that data. In a nutshell, SOAP is a network application protocol.A SOAP XML document instance, which is called a SOAP message,is usually carried as the payload of some other network protocol. For example, the most common way to exchange SOAP messages is via HTTP (HyperText Transfer Protocol), used by Web browsers to access HTML Web pages. The big difference is that you don’t view SOAP messages with a browser as you do HTML. SOAP messages are exchanged between applications on a network and are not meant for human

1.The SOAP XML document is also called the SOAP envelope.30166 04 pp079-126 r2jm.ps  10/2/03  3:56 PM  Page 8182 Chapter 4 SOAP consumption. HTTP is just a convenient way of sending and receiving SOAP messages.SOAP messages can also be carried by e-mail using SMTP (Simple Mail Transfer Protocol) and by other network protocols, such as FTP (File Transfer Protocol) and raw TCP/IP (Transmission Control Protocol/Internet Protocol). At this time, however, the WS-I Basic Profile 1.0 sanctions the use of SOAP only over HTTP.

Web services can use One-Way messaging or Request/Response messaging. In the former, SOAP messages travel in only one direction, from a sender to a receiver. In the latter, a SOAP message travels from the sender to the receiver, which is expected to send a reply back to the sender. Figure 4–2 illustrates these two forms of messaging.SOAP defines how messages can be structured and processed by software in a way

that is independent of any programming language or platform, and thus facilitates interoperability between applications written in different programming languages and running on different operating systems. Of course, this is nothing new: CORBA IIOP and DCE RPC also focused on cross-platform interoperability. These legacy protocols were never embraced by the software industry as a whole, however, so they never became pervasive technologies. SOAP, on the other hand, has enjoyed