Java Reference
In-Depth Information
Chapter 12. Web Service Interoperability
Introduction
A primary purpose of web services is to interoperate with other services, regardless of the
platform on which they are running or the language in which they are implemented. While
the WS-* specifications go a long way toward describing platform-independent mechanisms
for message exchange, the devil is in the details. As with any specification, there are many
areas of the WS-* specifications that are open to interpretation, and there are a numbers of
questions to which vendor platforms must determine the answers themselves. The specifica-
tions for XML, SOAP, and WSDL were written independently of one another, and therefore
have minor gaps and overlaps between them. Moreover, developers are free to implement ser-
vices in a variety of ways given the choices that the specifications make available, and that
makes interoperability more challenging. Between different transport layers, policy and secur-
ity implementations, message encoding mechanisms, platform-specific character encodings,
and differences in implementation details, interoperability can become a daunting task.
Let's look at this concretely. A WSDL describes a web service in general terms. It allows for
customizations, exposing implementation details (such as Java customizations), and a number
of combinations of transport and encoding mechanisms. It is perfectly acceptable to imple-
ment your service as RPC/encoded, which defines the format of messages over the wire. As
a developer starting from Java, you're not going to see any difference between an encoded or
a literally formatted message. However, some platforms have difficulty working with SOAP
encoding, and some elements of SOAP encoding are handled differently from one platform to
another. That makes RPC encoding a poor choice if you want to make sure as many people as
possible can use your service.
The challenge then becomes finding a suitable middle ground for service implementation so
that the greatest variety of platforms can consume your services. Enter the Web Services Inter-
operability Organization, or WS-I. The WS-I consists of representatives from a large number
of vendors, whose basic mission is to define standards to which web service implementations
should conform in order to ensure the widest possible audience for their services. The chief
product of the WS-I is the Basic Profile (BP), currently in version 1.2. At the time of this writ-
ing, however, version 1.1 of the Basic Profile probably still enjoys the widest support amongst
vendors.
The Basic Profile is a document that indicates the specific choices that you as a developer
should make when implementing a service to ensure interoperability with other service imple-
