Link on page 'http://www.libertex.com/site/links.html':
<a href="http://news.bbc.co.uk/story883488.stm" id="134">news story</a>

SOAP broken link fire-and-forget (single recipient) message

<?xml version="1.0" ?>
<env:Envelope xmlns:env="http://www.w3.org/2001/09/soap-envelope">
  <env:Body>        
    <r:BrokenLink xmlns:r="http://www.wibble.com/2005/11/broken-link">
      <r:referer>http://www.wibble.com/site/links.html</r:referer>
      <r:target>http://news.bbc.co.uk/story883488.stm</r:target>
      <r:response> <!-- optional -->
       <r:code>404</r:code>
       <r:text>404 - File Not Found</r:text>
      </r:response>
      <r:link>
       <r:id>134</r:id>
       <r:status>ReportedCheckedOK</r:linkstatus> <!-- link's status reported by web server -->
       <r:timechecked>datetime</r:timechecked> <!-- time last checked by server -->
      </r:linkid> <!-- optional -->
    </r:BrokenLink>
  </env:Body>
</env:Envelope>

1 Browser sends HTTP GET for URI to Webserver 1
2 Webserver 1 sends HTML page
3 User follows link
   3.1 User clicks link pointing at Webserver 2
   3.2 HTTP 404 response - target not found
   3.3 Display 404 page to user as usual
4 Browser sends SOAP message (above) to Webserver 1

Possible link status codes:
  Link unchecked
  Checked, ok, <datetime>
  Checked, broken, <datetime>
  Reported broken, unchecked
  Reported broken, Checked, ok, <datetime>
  Reported broken, Checked, broken, <datetime>

NB 1. SOAP messages are only sent if link status is either Unchecked or CheckedOK, and if the link response is 404
   2. Once message is received, it is expected that the webserver marks the link with ReportedBrokenUnchecked, to prevent other
      browsers from reporting it (could result in DDOS-like requests!)
   3. May want some sort of indication as to what protocol/XMLNS for broken links the server supports
   4. May want to enable server to automate the initial checking
   
-

Components required

1) XSD definition for this SOAP message
2) Firefox plugin for browser to detect 404's and send SOAP messages (to sites that support it)
3) Servlet to receive broken links and display broken links' info

Optional

1) Tomcat Filter to retrofit existing website with support for broken link highlighting
2) Java script client version (with rewrite support in above filter)
3) Way to indicate what broken link support is available, and how to tell if links are broken (pattern match or class=...