Xpointer Entity

Steve DeRose Steven_DeRose at Brown.edu
Wed Jan 20 15:43:44 GMT 1999

At 12:49 PM -0400 1/19/99, Ogievetsky, Nikita wrote:
>Is it (or will it be?) possible to use XPointer as Entity reference?
>This will allow me to generic element content, changing depending on
>children/ancestors surrounding... (so close to real life...)
>Of course it is dangerous as a source of circular references...
>- so it will be an extra burden for a parser.

I imagine you mean "in" the system identifier of an entity declaration, right?
For example,

<!ENTITY mysection SYSTEM

I hope and expect that will be the case; it's an obvious and useful
application. We discussed it during the development of XPointer. Of course
XPointer can't compel applications to support it; but it seems an obvious
thing to support if you're writing an app. It's also not really any more
work after you've built support for entities in general, and for XPointer
in general.

I think this adds no more problem for circular entity references, than is
already handled for entities in general (SGML prohibits circular entity
references, by the way). Anyway, they're not hard to catch.

<!ENTITY boom "&boom;">

SGML and XML have the limitation that entities have no parameters; one
advantage of is that any time you get a circular reference it must be
wrong, because the circle could never terminate. If entities were
parameterized somehow, then you could possibly have useful recursion that
eventually terminated; but they aren't, so you can't.

If you know of any implementations that support this usage, please send me
the info and I'll add them to my page about xpointer and xlink
implementations at


Steven_DeRose at Brown.edu; http://www.stg.brown.edu/~sjd
Chief Scientist, Scholarly Technology Group, and
   Adjunct Associate Professor, Brown University;
Chief Scientist, Inso Corporation

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