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Subject: Re: [emergency-comment] FW: [CAP] Unique Message Identifiers in CAP


Rex -

Is this really in order for the TC at this time, while we have a 
ballot pending?  Seems like it would be more appropriate to wait 
until we see what feedback we get from the balloting process and then 
work through all the issues that arise in a systematic fashion.

If we start taking up every individual comment as it's offered I'm 
afraid we're going to duplicate a lot of effort and get bogged down 
when we should be moving ahead on other projects.

(I'll also note that this and Mr. Wyman's other comments have been 
the subject of quite a bit of discussion in the CAP Working Group 
list.  If we're going to get into this right now, it might save some 
time for TC members to review the discussion in the archive at 
<http://www.incident.com/pipermail/cap-list/>.  But I still think it 
would be more proper to hold this in abeyance until the current 
ballot is complete.)

- Art


At 10:34 PM -0800 3/2/04, Rex Brooks wrote:
>Thanks, Bob,
>
>This raises an important issue that we should address. Since I have 
>been asked to chair that meeting for Allen, the TC chair currently 
>on vacation, due to the recent resignation of the designated 
>co-chair, unless other arrangements have been made today while I was 
>hunkered down in day two of four of the WSRP f2f meetings this week, 
>I will put this on the agenda, along with the severity/urgency and 
>the ALL CAPS examples issues, as well.
>
>Thanks again,
>Rex
>
>
>At 10:18 PM -0500 3/2/04, Bob Wyman wrote:
>>     The CAP specificiation, while saying that message identifiers are
>>supposed to be unique, doesn't say anything explicit about the scope
>>of the uniqueness. Normally, specifications for Internet protocols
>>make this explicit to avoid confusion and diverging implementations.
>>Is it expected that a message identifier is globally unique? (i.e. no
>>two senders should ever generate the same message identifier.) Or, are
>>these identifiers only unique for each sender? If only unique for each
>>sender, then should we assume that that *actual* identifier is
>>constructed by concatenating the message identifier with the sender
>>identifier?
>>
>>     In any system that relies on unique identifiers, it is important
>>to identify the time period during which uniqueness is guaranteed.
>>However, the CAP spec doesn't do this. Are senders allowed to reuse
>>identifiers? If so, under what circumstances? Is there, for instance,
>>an implied period of time during which the uniqueness of identifiers
>>should be maintained? (Note: NWS seems to reuse the same message
>>identifiers whenever they generate info for a particular area. Thus,
>>the message identifier "wwa_California" is reused in *every* CAP
>>message that they write concerning California. Is this what the
>>designers of CAP intended? (Note: I realize that NWS is still using
>>0.9a1, however, the general issue still exists.) Can/Should message
>>identifiers be reused? I would suggest that this should be strongly
>>discouraged. If message identifiers are constantly reused in the
>>manner that NWS does, then they aren't really "message identifiers" --
>>rather, they are serving the purpose of "subject," "topic," or
>>"series" codes.
>>     If it is important to be able to identify a sequence of unique
>>messages that all address the same subject then support for that
>>should be provided for in the specification rather than having people
>>overload a field which should be message-specific.
>>
>>     Because CAP message ids are assigned by senders, there are a
>>number of opportunities for severe confusion. For instance, it appears
>>to be difficult to take CAP feeds from both the NWS and California
>>EDIS without getting very confused about what is really happening. The
>>difficulty is caused by the fact that California repackages NWS
>>weather alerts as CAP messages which have different message
>>identifiers than the NWS CAP feed uses. Ideally, it would be possible
>>for the EDIS messages to at least identify the NWS messages that were
>>their source so that software could filter out duplicates. (Note: The
>>current "source" field is inadequate for these purposes.) The current
>>situation would force anyone who was reading both EDIS and NWS CAP
>>feeds to simply ignore all data that came from EDIS since it is
>>probably a duplicate of NWS data. This means that if California ever
>>issued its own "MET" alerts, not simply copies of NWS data, readers
>>would probably ignore them. This is not good.
>>
>>         bob wyman
>>
>>
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>
>
>--
>Rex Brooks
>GeoAddress: 1361-A Addison, Berkeley, CA, 94702 USA, Earth
>W3Address: http://www.starbourne.com
>Email: rexb@starbourne.com
>Tel: 510-849-2309
>Fax: By Request
>
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