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Re: [emergency-msg] CAP Channels

  • 1.  Re: [emergency-msg] CAP Channels

    Posted 08-12-2003 00:29
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    Subject: Re: [emergency-msg] CAP Channels


    Rex -
    
    >I get the feeling that I am supposed to be seeing formatted display 
    >instead of code, but I don't know for sure, so I'm just asking.
    
    You should be receiving an XML document with a <channel> root element 
    and (most of the time) a few <item> elements... like this:
    
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
    <channel xmlns="http://www.incident.com/channel";>
       <title>California EDIS Bulletins</title>
       <channelUrl>http://www.edis.ca.gov/cap_0.9/index.xml</channelUrl>
       <contact>acb@incident.com</contact>
       <channelUpdated>2003-00-11T12:50:45-07:00</channelUpdated>
       <item>
         <format>http://www.incident.com/cap/0.9a1</format>
         <identifier>106062122011743</identifier>
         <sender>EDIS@edis.oes.ca.gov</sender>
         <topic>EDIS DAILY SYSTEM TEST</topic>
         <sent>2003-08-11T10:00:00-07:00</sent>
         <posted>2003-08-11T10:00:00-07:00</posted>
         <expires>2003-008-11T16:00:20-07:00</expires>
         <itemUrl>http://www.edis.ca.gov/cap_0.9/1060621220.cap</itemUrl>
       </item>
       <item>
         <format>http://www.incident.com/cap/0.9a1</format>
         <identifier>106061785031416</identifier>
         <sender>xsjoes@edis.oes.ca.gov</sender>
         <topic>TEST</topic>
         <sent>2003-08-11T09:04:00-07:00</sent>
         <posted>2003-08-11T09:04:00-07:00</posted>
         <expires>2003-008-11T15:04:10-07:00</expires>
         <itemUrl>http://www.edis.ca.gov/cap_0.9/1060617850.cap</itemUrl>
       </item>
       <item>
         <format>http://www.incident.com/cap/0.9a1</format>
         <identifier>106063144418022</identifier>
         <sender>laoem@edis.oes.ca.gov</sender>
         <topic>LA COUNTY HEAT ADVISORY</topic>
         <sent>2003-08-11T12:50:00-07:00</sent>
         <posted>2003-08-11T12:50:00-07:00</posted>
         <expires>2003-008-11T18:50:44-07:00</expires>
         <itemUrl>http://www.edis.ca.gov/cap_0.9/1060631444.cap</itemUrl>
       </item>
    </channel>
    
    What appears on your screen depends on how your browser handles 
    text/xml responses... some parse them and lay them out, while others 
    suppress the tags and you need to View Source to see the whole thing. 
    (That's what I have to do in Safari, for example.)  The .cap files 
    return from that server as text/plain so they may be more 
    browser-friendly.
    
    Remember that the channel file isn't intended for a browser... it's 
    meant for an XML-aware client in an automated process.  A human with 
    a browser does just fine with a directory listing... although how 
    many humans want to look at raw CAP XML anyway?
    
    >As to the RSS-like indexing, I'm also at a loss as to why this is desireable.
    
    Think about how you'd support an automated process that polled for 
    new messages.  You could build all the current messages into one big 
    file and make every client download every message every time, but 
    that would be inflexible and relatively inefficient.
    
    Alternatively you'd need to provide at least the filenames for 
    available messages... and once you've done that it wouldn't be a lot 
    more work to provide a few details that let the client decide which 
    messages it wanted to download.   And then you could use the same 
    format for aggregation, filtering and even discovery.
    
    >However, I would think that a simple Web Services Registry lookup 
    >either in UDDI or ebXML would do the job handily in finding a 
    >service, and then registering it so that when one fires up a 
    >connection to that service, one gets the info (portlets in portals 
    >in the model I use most) in the format desired, be it html, xml, 
    >voiceXML, etc.
    
    I'd agree... except maybe with describing that approach as "simple." 
    Certainly this whole arrangement could easily be described in WSDL 
    and registered in UDDI and/or ebXML.  But even then, seems like many 
    request-response (including archival) services might get performance 
    gains from indexing.
    
    >This doesn't require considering whether the messaging requested by 
    >the receiver is either push or pull since receivers don't receive 
    >anything until they ask for it. One can set up an automatic 
    >connection where appropriate so that the needed info is always 
    >there, and it can be set up to perform whatever kind of alert is 
    >required.
    
    Did I neglect to stress that this idea doesn't preclude more 
    sophisticated implementations, if and when we have the 
    infrastructure?  It's just that at least a couple of actual CAP 
    content providers have already expressed a need for a truly simple 
    way to expose their messages, particularly in the near term.
    
    - Art
    
    


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