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Subject: CAP over Atom (Please review)

At PubSub.com, we’ve started generating “CAP over Atom” files. By this I mean CAP messages which are encapsulated in Atom Feed Files as defined in: http://www.mnot.net/drafts/draft-nottingham-atom-format-02.html  . We’ve started with CAP encodings of the Earthquake data that we’ve been working with recently.

The Atom format, which is currently being updated and redefined in the Atom-Pub IETF Working Group, is widely understood and processed by “RSS news aggregator” software. We’re using this format as a “packaging” format for streams of CAP messages since no other widely implemented formats really seem appropriate for the task and since CAP itself defines no such “stream” format. In any case, providing CAP data wrapped in the Atom format means that the millions of people who have news aggregators will be able to view CAP messages with no requirement to update or obtain new software. (Although better display and information will be provided by news aggregators that actually understand the CAP format…)

In order to provide the minimum elements required by Atom and to ensure that news aggregators have useful information to display even if they don’t understand the CAP format, we are forced to copy a number of the CAP elements into Atom elements. I believe any application of “CAP over Atom” will be required to do much the same. The duplication of data is unfortunate, but necessary. If “CAP over Atom” is accepted as something which is useful, it might be a good idea to generate a set of general guidelines for packaging CAP in Atom feeds.

What we’ve done is:

1.       Copied alert:info:headline to atom:title.

2.       Copied alert:info:description to atom:summary

3.       Copied alert:info:web to atom:link

4.       Generated an atom:id based on the CAP incident id using the tagUri scheme. See: http://www.taguri.org/


For a sample Atom feed containing CAP messages which describe recent earthquakes, please see:


Note: If you view the Atom feed above in a web browser, the result may not be terribly pleasing… We’re still working on the style sheet. – Please pay attention only to the source of the feed… (i.e. do “View Source”).

I would appreciate any comments you might have on our use of Atom as a packaging mechanism for streams of CAP messages.

            A sample atom:entry from the Atom Feed above appears below:




<title><![CDATA[ Earthquake: M 1.6 (D) NORTHERN CALIFORNIA 2005-02-04T02:00:43.100Z ]]></title>




<link rel='alternate' type='text/html' href='http://earthquake.usgs.gov/recenteqsUS/Quakes/nc51156375.htm'/>

<summary>An earthquake occurred at 2005-02-04T02:00:43.100Z. The magnitude 1.6 event has been located in NORTHERN CALIFORNIA. (This is a computer-generated message and should not be considered authoritative.) </summary>

<content type='text/xml'>

<alert xmlns="http://www.incident.com/cap/1.0">














        <senderName>Pubsub Earthquake Service</senderName>

        <headline>Earthquake: M 1.6 (D) NORTHERN CALIFORNIA 2005-02-04T02:00:43.100Z</headline>

        <description>An earthquake occurred at 2005-02-04T02:00:43.100Z. The magnitude 1.6 event has been located in NORTHERN CALIFORNIA. (This is a computer-generated message and should not be considered authoritative.) </description>




        <parameter>Magnitude=1.6 MD</parameter>

        <parameter>Depth=2 km</parameter>



          <areaDesc>2 km depth at latitude 38.8168, longitude -122.7915 at location: NORTHERN CALIFORNIA</areaDesc>

          <circle>38.8168,-122.7915 0</circle>








1.       We’ve set the status of all messages to “Test”…

2.       We’re uncertain how to determine the values for urgency, severity, and certainty. Thus, we’ve set them all to “Unknown.”

3.       We are using the same value for identifier and incident. This appears to be reasonable… Is it?


This service compliments the Earthquake service that I recently mentioned on this list. We will be publishing both raw Earthquake messages/feeds as well as CAP messages/feed in the future. These two formats are targeted at different audiences.

            Once we’ve done a bit more testing, we’ll announce how to access the user interface to create custom subscriptions to these feeds.


Your comments and/or suggestions would be appreciated.


                        bob wyman



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