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

[Rex Brooks <rexb@starbourne.com>]

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
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