narrowing a DTD

Bill Wadley bill at
Thu Apr 1 14:12:48 BST 1999


I would like to take a currently existing DTD (e.g. Scalable Vector
Graphics, SVG), _overlay_ some different semantics onto it, and create a
subset of the SVG DTD.

I would like to create a SVG document that is 100% SVG with no new
ELEMENTS, ENTITIES or anything. However, I'm creating this document from
some other data structure that does not map 1:1 to SVG. I would like this
*mapping* to be a *standard* in it's own right for use in a particular
community. Essentially, I would like an SVG-like DTD, a pure subset with
different semantics, that would be used to create the SVG-overlay document.
The full SVG DTD can still be used to *extend* the SVG-overlay DTD, but
when we go to parse the SVG-overlay document, we can ignore the extended
SVG and just go for the SVG-overlay stuff knowing that the creator of the
document used the SVG-overlay DTD and that the ELEMENTS and things mean
what we think they mean. On the other hand, we can pass the SVG document
and the full SVG DTD to an SVG drawing program, and it will have no
problems just drawing the picture as usual.

So that is what I want; question is, how do I do it? My immediate response
is to take the SVG DTD and start removing things, but that's not enough. We
need to use some of the CDATA attributes to hold specific information in a
specific format; this would imply that we need to "override" declarations
in the original DTD somehow. It may also be necessary to increase the
restrictions on ELEMENT declarations. Nothing needs to be added or
relaxed. (If this weren't not true, I would say all is lost, but this is a
narrowing, not a broadening.)

I'm trying to be concise, but if I'm not being clear, I'll be happy to try

Any light shed on this problem will be greatly appreciated.



Bill Wadley     |GAT/d-(++) s++: a C++++ UL++++$ P++++$ L+++>++++ E- W+++$   |
bill at |N+++ w-- O-- M-- PS+ PE Y++ PGP++ t++ 5++ X- R+ tv b++++ D++| |G++ e* h--- r+++ y?      |
"The dinosaurs became extinct because they didn't have a space program."
                                                          -Larry Niven

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