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Re: Re: 3 XML Design Principles

• To: "Bullard, Claude L (Len)" <len.bullard@i...>
• Subject: Re: Re: 3 XML Design Principles
• From: Jeff Rafter <lists@j...>
• Date: Mon, 31 Jan 2005 13:23:30 -0700
• Cc: "Roger L. Costello" <costello@m...>, xml-dev@l...
• In-reply-to: <15725CF6AFE2F34DB8A5B4770B7334EE07206B9B@h...>
• References: <15725CF6AFE2F34DB8A5B4770B7334EE07206B9B@h...>
• Reply-to: lists@j...
• User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)

> Same for VRML and X3D.  It has route structures.   I tend to think of it as
> a network of objects, not a hierarchy.   X3D has a hierarchy in the
> XML encoding because it has to have a root node.  In the VRML, encoding,
> it doesn't.   USE nodes provide, define one use everywhere functionality.
> There is a hierarchy of objects with some inheritance of properties, and
> to nest finite coordinate spaces.   X3D like VRML likes a one pass parse.

I was actually thinking of bringing up a very similar example in SVG. In 
SVG 1.1 you have a <use> element that can refer by id to a defined 
graphic primitive. Certain attributes of the <use> are passed on to the 
conceptual copy of the primitive (say a polyline). While this cuts down 
on repeated data throughout the SVG document it is wildly complex to 
process.

One must understand the notion of a conceptual graphic, a shadow tree, 
and a realized version of the document when rendered. This is 
exacerbated by interactivity-- when an object that was <use>d is clicked 
you must find the conceptual node correlating to the position clicked, 
then find the corresponding <use> element and ultimately pass a third 
interface to the conceptual primitive using an SVGElementInstance.

Once you have all of that figured out you then have to worry about 
mutation events in either the <use> or the element to which the <use> is 
referring (i.e., both ends of the relationship must be monitored for 
changes). This ultimately leads to a lot of jumping around in the 
processing. It is confusing at best.

When working with <use> elements the first question I ask of document 
creators is "Do you *really* need them".

I wasn't sure exactly how to tie this back to Roger's post-- so thanks 
Len for giving me the stepping stone.

Cheers,
Jeff Rafter

• References:
  • RE: {Spam?} Re: 3 XML Design Principles
    • From: "Bullard, Claude L (Len)" <len.bullard@i...>

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