- From: Kim Marriott <marriott@mail.csse.monash.edu.au>
- Date: Tue, 17 Jul 2001 17:05:55 +1000
- To: www-svg@w3.org
- cc: marriott@indy10.csse.monash.edu.au, bernd.meyer@acm.org, tardif@cs.monash.edu.au
We would like to circulate for discussion a proposal on including constraint-based specifications into the the next revision of SVG. The main advantage of using constraints is that they allow the designer to declaratively specify relationships between components of an SVG document, rather than having to precisely specify their layout or position. For instance, that a box is big enough to contain some text or that a line connects two circles. Adding constraints to SVG means that the SVG author can specify flexible readjustment of layout in response to viewer requirements, such as large fonts, and the viewing environment such as a small browser window on a PDA. In particular constraints allow differential scaling of SVG document elements, and alternate layouts depending on the viewing context, thus increasing the accessibility of SVG documents. Another important advantage of constraints is that they provide support for user interaction and animation. Bernd Meyer, Laurent Tardif and I have prepared a paper discussing the potential benefits of constraints and possible ways they could be added to SVG. It can be found at http://www.csse.monash.edu.au/~tardif/CSVG/paper.html This discussion paper explains through several examples how constraints are a natural extension to SVG 1.0 which will add significant capabilities at relatively little implementation or performance cost. We first motivate the need for constraints by arguing that SVG should allow flexible re-adjustment of diagrams at display time. We discuss in detail how one-way constraints can achieve this and also how they facilitate the specification of animation in SVG. We next consider interaction. For this purpose one-way constraints are not sufficient and more powerful multi-way constraints are needed. We discuss the various classes of constraint solving algorithms and how the implementation of the suggested SVG extension can be based on these. This discussion paper is intended as a submission to the SVG 2.0 working party. Its primary purpose is to stimulate discussion.... Kim Marriott
Received on Tuesday, 17 July 2001 03:06:01 UTC