htm residing at the
path /bob/ on the web server www.bob.com. The address is
both a unique identi?¬?er and a way to retrieve the page. The
same mechanism could be used for web services, and in fact
this is common practice in many applications. However, this
does not play very well with web services??™ attempts to be independent
from the underlying technology. HTTP mandates the
use of one speci?¬?c protocol, whereas the web service should be
able to be moved on some other transport without dependencies.
WS-Addressing provides a richer way of referring to web
services, helping to overcome the previously mentioned limitations
and supplying the more expressive model that is required
by the other advanced WS-* speci?¬?cations.
WS-Policy
WSDL describes the operations offered and the message formats
required by a web service, but it does not give further details
about any other requirements associated with the web service
invocation. For example, a web service implementing a wire
transfer may be invoked with the correct message format, but
WSDL describes the
kind of messages
that a web service
accepts and
produces
WS-Addressing
provides a rich way
of referring to a
web service
WS-Policy advertises
what is necessary
for calling a
web service while
satisfying its requirement
WS-* Web Services Speci?¬?cations: The Rei?¬?cation of the Identity Metasystem 145
the software will not execute the operation unless the caller
identi?¬?es itself using a certain authentication technique.
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