Who Cares About UDDI?
David Chappell - April
25 , 2002
Web services are the most important thing happening
in distributed computing today. And since distributed computing
has become the norm, that puts them high on the list of important
things, period. As usually described, the trinity of Web services
technologies includes SOAP for invoking remote operations, WSDL
for specifying what those operations look like, and UDDI for . .
. well, what, exactly? What is UDDI actually good for?
Theoretically, UDDI stores information that helps
clients select and use a web service. This might mean information
about the kind of service provided, who provides it, and potentially
even how much it costs. UDDI is a very open-ended technology, and
so it can store all kinds of data. Pragmatically, however, the main
thing required to access a Web service is its WSDL definition. Tools
such as Microsofts Visual Studio.NET and IBMs WebSphere
Studio can read a WSDL file and generate the client proxy required
to invoke the operations described in that file. While there are
UDDI servers available on the Internet today, theres not much
in them. In particular, they dont contain many WSDL files.
This isnt really too surprising. After all,
the primary application of Web services today is enterprise application
integration (EAI). Connecting existing code is a pressing business
problem, one solved quite effectively by Web services, and staying
inside the firewall lessens the challenging authentication and privacy
issues that can accompany SOAP today. For both of these reasons,
EAI has proven to be the killer app for Web services. Yet EAI interconnections
are quite static, and they dont generally require Internet
access. Accordingly, todays Internet-based UDDI servers are
largely irrelevant to the problem. There are simpler ways to discover
the WSDL interface of the desired Web services, such as having it
sent to you via email by your fellow developer on the project.
The next most important category of Web services
applications today is probably business-to-business, or B2B, integration
across the Internet. Internet-based UDDI servers could potentially
be more useful here. Once again, though, todays B2B interactions
are generally quite staticbusiness partners agree in advance
to communicateso theres no need for the very general
service that UDDI can provide.
So when would UDDI be useful? One possibility is
applications running in a world of widely available Internet-based
Web services, with searches and frequently changing connections
the norm. Here, UDDIs very general capabilities to describe
whats available and to provide the information needed to choose
and communicate with the appropriate service might be useful. But
dont hold your breath waiting for this world to arrive: it
wont be here anytime soon. Dynamically discovered Web services
face a host of problems, including security, market demand, and
charging mechanisms. While some Web visionaries tout the inevitability
of this world, I confess to some skepticism. It may never arrive.
UDDI might also be useful as an intranet-based
service, one that could be used to learn about locally available
services. This is a more plausible alternative, but still not one
for which any substantial need exists today. Intranet-based projects
typically dont change that often, and so a specialized directory
service is probably more trouble than its worth.
Given UDDIs problems, its fortunate
that a more recent specification produced jointly by Microsoft and
IBM provides a simpler, cleaner answer to the core problem of finding
WSDL definitions. Called WS-Inspection, it defines a straightforward
XML document structure for finding either a WSDL file for a particular
Web service or its UDDI description. While WS-Inspection isnt
yet widely supported, it looks likely to become an important part
of the Web services technology arsenal. And while UDDI may one day
be a useful standard, it has so far remained the least important
of the big three Web services technologies.
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