Re: [xsl] Revision Marking in HTML

Subject: Re: [xsl] Revision Marking in HTML
From: Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>
Date: Tue, 26 Apr 2005 12:35:10 -0400

While you are trying to apply David's solution I'd recommend you also test XMetaL to see whether the assumption he makes in his code (the PI pairs are "well-balanced" with respect to element markup) is correct, or whether XMetaL cannot in fact insert such a PI wherever it likes, thereby breaking the implicit "containment" and presenting, in effect, an overlap problem. (The "virtual" elements demarcated by the PI-pairs overlap the XML's own element structures.)

While I haven't myself tested XMetaL for this, I fear and suspect this is the case.

Overlap problems are notoriously hard for XML technologies in general, and there is a considerable (and growing) literature on the topic. It's sometimes referred to as "multiple concurrent hierarchies". The various approaches to dealing with this vary quite a bit depending on the actual processing requirements for the system (e.g. projects that work with stable and complete datasets can do things very differently from systems that have to deal with new data all the time), and include proposals to step outside XML altogether. This is because, better than any other example I can think of in XML tech, they demonstrate the engineering principle (or Cosmic Law of Compensation, if you prefer) that where there's a gain, there's a loss. In this case, XML's clumsiness at dealing with this (or more precisely, XSLT's) is a consequence of our establishing the tree as our data model of choice.

Keywords you might Google:

markup overlap
multiple concurrent hierarchies


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