[INFOD-WG] Dynamic consumer constraints

[Dieter Gawlick]

All line references are from the published Base INFOD Specifications - 
see Current Documents folder

Property Constraints (line 991) are used to derive Consumer Entry 
References (line 1788); Dynamic Consumer Constraints are past along to 
publisher in the Dynamic Consumer Constraints (line 1791).

The specifications do allow that both types of constraints are specified 
concurrently, they do not say what the combination means. So, one 
possibility is to say: If both constraints are specified all messages go 
to consumers listed in the Consumer Entry References *and additionally 
*to the consumers that fit the Dynamic Consumer Constraints. Both 
entries and the Registry notification to the publishers are used. If we 
would like the Registry to provide the set of all possible consumers 
(for the Dynamic Consumer Constraints) we would have to add an entry in 
the notification.

Calculating this list, however, seems to create fundamental problems; it 
may be very big and more importantly the registry may not understand the 
constraints because these constraints are referencing data vocabularies, 
which do not need to be XML vocabularies. So far, we avoided the 
registry to get involved in evaluating non-XML constraints.

We could also say that property constraints limit the eligible dynamic 
consumers; but this would have to be made very explicit.

I recommend not to calculate the list of potential consumers and clarify 
the specifications in this respect.

If we go this direction we do not have a solution for the publisher to 
become aware of new consumers for an existing message.

However, here is a proposal for future versions: We specify that the 
registry has to support CQs (Continuous Queries). If a publisher likes 
to be informed about new consumers with a set of properties the 
publisher has to write a CQ against the registry. Obviously, we could 
also say that the registry has to accept subscriptions - CQs and 
subscription seems to be very closely related. We already had this in 
the specifications and removed in the NY F2F since we felt that the 
implementation is too difficult.

Dieter
-- 

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Dieter Gawlick | Architect | 650.506.8706
Oracle Server Technologies
500 Oracle Parkway | Redwood Shores, CA 94065
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