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<< ... a large, ebXML-based registry ....
... not a big believer in large, centralized, heavyweight anything,
especially if it's targeted for the Web. I would like to present to my
client the idea of a distributed registry based upon RDDL collections.
If you're building for eBiz "in the large" then scalability is a legitimate
concern. Your desire is to avoid a centralized registry because of performance,
reliability, and possibly security issues. Don't we have similar issues if the
whole eBiz world adopts your RDDL model? There have already been some
discussions here about common namespace overloading, RDDLCache and a
RDDLSecurityLayer.
<< But we need a mechanism to store info about each service.
If we're going to eventually deploy web services on a massive scale, we'll
undoubtedly exploit distributed registries and grid computing. Some of the
technical work has already been done. The Open Grid Services Architecture (OGSA)
and Web Services Discovery Architecture (WSDA) are two solutions for exploiting
grids for the new service architectures, for
distributed registries, etc.
They provide a basis for addressing ebXML registry requirements such as filtered
and browse query capabilities. Instead of
being tied to an API, such as UDDI's find_service, you can also use a solution
such as XQuery or XPath. ebXML has a submitAdhocQuery method and optional SQL
queries. The ebXML registry team has also been adding features such as
content-based queries, iterative queries, event notification, and federated
registries.
OGSA combines grid computing and web services. It defines standard interfaces
such as Discovery and Factory, with the factory registering each instance of a
service with the registry. IBM is driving OGSA, although it isn't clear
Microsoft, Sun or HP will jump on the OGSA bandwagon. There is an Open Grid
Services Working Group that recently released a
specification for OGSI, a a grid services infrastructure:
www.gridforum.org/ogsi-wg/drafts/draft-ggf-ogsi-gridservice-04_2002-10-04.pdf
OGSI provides multiple techniques for finding services (queryByServiceDataName,
XPath and XQuery). It provides
notification messages and subscriptions by service name and the registry
supports discovery via a WS-Inspection document.
WSDA is a product of work at CERN. It has interesting characteristics such as
using Simple WSDL, HTTPS and BEEP. For service discovery on a large scale, it
can integrate with a P2P database network or multi-domain grid (e.g.,
http://ccwp7.in2p3.fr/mapcenter/datagrid-s/). There's more than one level of
registry and the top level must support an XQuery interface. For a UDDI
scenario, for example, a WSDA developer could use a Presenter interface
or XQuery interface instead of the UDDI inquiry APIs. There will be a
presentation about WSDA at the Supercomputing conference in November:
http://www.sc2002.org/program_tech.html#
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