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Re: KML is very extensible ... but why?

  • From: Eliot Kimber <ekimber@contrext.com>
  • To: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>
  • Date: Fri, 20 Apr 2018 12:19:41 -0500

Re:  KML is very extensible ... but why?

DITA has a similar feature, it’s “foreign” element.


The purpose is to allow embedding of non-DITA content with a clear signal that it is non-DITA. There is no expectation of interoperability for non-DITA stuff but the fact that’s non-DITA is clearly signaled.


With DITA 1.3 the DITA standard includes the integration of two non-DITA vocabularies, SVG and MathML, using this mechanism. So for those foreign vocabularies there is reasonable expectation of interoperation (meaning we know that most publishing tools support SVG and MathML to some degree).


The KML feature requires the use of a non-KML namespace, so that seems to be the equivalent “this is not part of the standard” signal that DITA uses the <foreign> element for.


I think that’s very different than just allowing the addition of new elements or attributes without any clearly-defined way to indicate that the new things are not part of the core vocabulary definition.






Eliot Kimber




From: "Costello, Roger L." <costello@mitre.org>
Date: Friday, April 20, 2018 at 11:59 AM
To: "xml-dev@l..." <xml-dev@l...>
Subject: KML is very extensible ... but why?


Hi Folks,


The format of KML 2.3 documents are specified with a W3C 1.1 XML Schema. XML Schema 1.1 has a powerful feature which KML uses. At the top of the KML schema is this:

  <defaultOpenContent mode="interleave">
      <any namespace="##other" processContents="lax"/>

Read as: "KML documents are open. That is, XML elements from any non-KML namespace can be inserted before and after every element in KML documents. Those non-KML elements do not have to validate against any schema."


That makes KML very extensible.


But why?


If I add non-KML stuff in a KML instance, who’s going to understand my stuff? Google Earth? No. Google Maps? No. NASA WorldWind? No.


Only applications that have been custom-coded to understand my stuff will be able to do anything with it. Right? Doesn’t that destroy KML as a global geographic annotation/visualization language since now you’ve got all these non-interoperable dialects floating around?






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