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Subject: RE: [wsrp-interop] Original Emails on event QNames

Kevin brought up a very interesting point regarding event aliases during our
WSRP meeting.  Take the following use case:

a) Portlet A published Event A aliased to B
b) And Portlet B generates and subscribes to Event B
During the meeting, the following thoughts were offered:

a) Event A should be sent to portlet B as Event A NOT modified
b) Event A is renamed to event B but the payload is NOT modified (most
c) Event A is renamed to event B and the root element is renamed to event B
d) What does the schema for an event look like with aliases? Is the element
under the payload defined in the schema or just its type?

If you read the spec now regarding aliases:

aliases: An array of the QNames of events known to be semantically
equivalent to this event. While this can provide a hint to the Consumer
concerning potential items that could be correlated with this event, it
remains the Consumer's responsibility do any transformations required to
produce the described event.

To me, this sounds like if portlet A generates Event A, the consumer will
transform the Event A and its payload to Event B and send it to portlet B.
Therefore, portlet B only see Event B and the payload it expects.  This tell
me that aliases are just a "hint" as to what the payload could be
transformed to but the consumer is responsible for the mapping and it's
purely optional; portlet B might never get an event if the consumer does not
care to map these two events even if aliased.  This is just another
interpretation of how aliases affect events based on reading the description
of aliases in the specification. 

Given the varied interpretation on implementations, it appears there is
quite a bit of confusion on how aliases work.  Therefore, I think we need to
agree on the answers to some basic questions first:

a) What's the problem aliases are trying to solve?  What are the use cases
for aliases?  
b) Are aliases a hint as to what other events a given event can be
transformed into?  
c) Is it strictly a consumer transformation? A predetermined transformation
(e.g. change the name of event, change the root payload element name, etc.)?

d) Is it optional or required to send the event if there is a match on
e) Who's aliases are used?  The generating portlet, the handling portlet,
both?  Note the spec. indicates both generated and handled events need to be
described which brings up other inconsistency problems.
f) Can an event map to more than one target event via aliases?
g) What effect do aliases have on opaque payloads and wildcard subscribed
events if any?

Can we discuss these questions in one of our next scheduled meetings?


-----Original Message-----
From: Nathan Lipke [mailto:nathan.lipke@oracle.com] 
Sent: Thursday, October 22, 2009 11:38 AM
To: wsrp-interop@lists.oasis-open.org
Subject: [wsrp-interop] Original Emails on event QNames


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