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From: Paul Denning <pauld@mitre.org>
Date: Thu, 08 Jan 2004 15:15:05 -0500
Message-Id: <>
To: www-ws-arch@w3.org

Here is the proposed section to add to the WSA [1] to discuss Federation 
for Web Service Discovery.
This fulfills my action item.

Propose a new section: numbered 3.1.4 to follow 3.1.3 [2] "Discovery 
Service: Registry or Index?"

3.1.4  Discovery Service Federation

Although the registry viewpoint is a more centralized approach to discovery 
than the index approach, there will arise situations where multiple 
registries exist on the web.  It is expected that multiple indexes will 
also exist.  In such an environment, web service requesters that need to 
use a discovery service may need to obtain information from more than one 
registry or index.  Federation refers to the ability to consolidate the 
results of queries that span more than a single registry or index.

A registry or index may contain information about other registries or 
indexes to help support federation.  For example, a registry dedicated to 
air travel services may know about another registry dedicated to rail 
travel services.  I third registry for general travel services may contain 
information about some travel services, but may look to other registries 
for certain categories of services.  A search of the general travel 
registry may return a referral to the requester pointing them to the rail 
travel registry.  Federation of results in this scenario, as contrasted to 
the referral, would require the general travel registry to submit a query 
to the rail travel registry on behalf of the requester.  The general travel 
registry would then merge the results of the query to the rail travel 
registry with the results of a query to its own registry.  The general, 
rail, and air travel registries may need to share a common taxonomy or 
ontology to avoid forwarding inappropriate queries to other registries.  In 
this scenario, we assume the general travel registry examined the query 
from the requester and therefore did not forward the query to the air 
travel registry.

The general travel registry could have discovered the rail travel registry 
using a spider or index approach.  An indexing engine could have come 
across a registry, and based on the information it harvested from the 
registry classified it as a rail travel registry.  An alternative approach 
would be for the rail travel registry to publish information to the general 
travel registry and using the shared taxonomy could classify itself as a 
registry for rail travel services.

Note that each registry or index may provide a web service for discovery, 
so it may be appropriate to use a choreography or orchestration description 
language to describe the exchanges among these services needed for federation.



Received on Thursday, 8 January 2004 15:18:58 UTC

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