consolidated use cases and discussions for Issue 6917

I thought it might be a good idea to collect previous use cases and
discussions related to this issue to solicit group feedback on which
direction to pursue.

1. Performance Problem
This is raised by Mr. Ben Kloosterman in Issue 6917
(http://www.w3.org/Bugs/Public/show_bug.cgi?id=6917) regarding the
efficiency of content-based X-Path filter in WS-Eventing spec. To avoid
the expensive X-Path evaluations, he says several WS-Eventing
implementations invented their own topic mechanism. 

The concept of topic is also informally used in current WS-Eventing spec
samples (Example 4.1
http://www.w3.org/2002/ws/ra/edcopies/wseventing.html#Table4 and Example
5.1 http://www.w3.org/2002/ws/ra/edcopies/wseventing.html#Table13).

Mr. Kloosterman therefore suggests WS-RA to standardize a topic filter
to optimize event filtering and routing.

2. WS-Topic Discussion
There were some discussions on the relationship between WS-E and
WS-Topic from OASIS by Gil and Johannes Echterhoff
(http://lists.w3.org/Archives/Public/public-ws-resource-access/2009Apr/a
tt-0151/00-part). 

Basically, Mr. Echterhoff said WS-E does not support topic based
subscriptions and mentioned OASIS WS-Topic as a potential solution.

3. Dynamic Resource Problem
Issue 6425 http://www.w3.org/Bugs/Public/show_bug.cgi?id=6425) described
some CSTA uses cases related to the concept of topics. In CSTA ECMA-348
web services, for a computing function (event sink) to receive events,
it has to create a monitor on the switching function (event source)
using a service request. The set of event types the switching function
can generate are defined in the WSDL, but the set of events a monitor
can generate depends on the monitor filter, which is specified in the
monitor creation message. When a monitor is removed (by either event
source or sink), the event sink ceases to receive events from that
monitor. 

To address this issue, we proposed to address event source by
WS-Addressing EPR and model such monitors as part of the EPR. The issue
was FIXED and CLOSED without specifying how the EPR is extended to
include such monitors.

After revisiting the topic issues, it seems possible to also model such
monitor as a special topic. 

4. Possible Solutions
Given these uses cases and discussions, there seems to be the following
solutions suggested by various people so far:

4.1 Do nothing
We could claim these use cases are outside the scope of WS-E and leave
them to the implementations to extend WS-E or compose it with other
specs, e.g. WS-Topic.

4.2 Propose a simple topic mechanism 
Here we need to consider these issues:
a) how topics are advertised and linked with event types in WSDL
b) how topics are represented in subscribe messages (in EPR or filter)
c) how topics are associated with notifications 
d) how topic lifecycle is managed

4.3 Adopt WS-Topic with profiling
Describe a subset of WS-Topic and how to compose it with WS-E.


Li Li

Received on Tuesday, 26 May 2009 17:35:08 UTC