All the nonbasic WS-* speci?¬?cations
leverage this mechanism.
Figure 2-3 A simple XML document
SOAP de?¬?nes the
message envelope
format used for
communicating
with a web service
SOAP is extensible
by design
WS-* Web Services Speci?¬?cations: The Rei?¬?cation of the Identity Metasystem 143
Header
Body
Figure 2-4 A simple SOAP message
Simple Object Access Protocol? Not Anymore
At the time of its ?¬?rst formulation, SOAP was intended as a mean of accessing
remote objects across platforms. In this, it was following the footprints of its
predecessor, the XML-RPC speci?¬?cation. (RPC stands for Remote Procedure
Call.) Hence, the original SOAP term was an acronym of the expression Simple
Object Access Protocol.
As the idea of web service got further re?¬?ned, it became clear that thinking of
software in a remote location in terms of objects was not the best way of dealing
with distributed systems. The idea of an object implies a certain degree of control
from the caller, whereas in practice remote software is often entirely beyond
the sphere of in?¬‚uence of its clients. Without going into too much detail here,
web services moved away from the idea of exchanging objects as parameters
and return values.
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