EMBED and validation

Peter Murray-Rust peter at ursus.demon.co.uk
Sat Nov 29 16:02:50 GMT 1997

At 10:09 29/11/97 -0500, Eve L. Maler wrote:
>I don't think I've seen it explicitly suggested here, so here goes.  If you
>want to ensure that what's pointed to is real XML, and "belongs" in that
>location, how about using a plain old external text entity?  With a
>validating XML processor, you can guarantee that (a) the entity will be
>expanded in place before it even gets to the application and that (b) it
>will be validated in context.

Thanks Eve - this is undoubtedly the simplest way of 'including' things and
a key feature of XML. This needs promoting as much as possible, and
application writers and authors should try to build entity management into
their systems.
(I am waiting for more experience to see exactly what people want, but I
expect to add this to the JUMBO editor).

The only area of fuzziness is what the default and optional behaviours of a
parser (sic) are. If I write:

<!DOCTYPE HTML SYSTEM "html20.dtd" [
<!ENTITY pythagoras SYSTEM "pythagoras.xml"> <!-- in MathML -->
<P>This is Pythagoras' theorem:<BR>

and I run it through a parser what will happen? The answer is
parser-dependent. It might:
	- always include and validate external entities in which case there will
be a validation error (MathML uses a different DTD from HTML). If the
entity is valid, then it creates a 'single document' which is easy to
search, etc. One disadvantage is that (for Java) the document could get too
big for the JVM.

	- offer a commandline switch that allows inclusion of external entities OR
defers their expansion to the application/processor. In that case the
*application* has to be able to able to run a parser over the 'included'
(JUMBO can do this at present - it can even use a different parser from the
initial one, which may be useful if they have different behaviours).


Note, of course, that an application may  also want to run a validating
parser over the targets of HREF and JUMBO can do this as well.

Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary

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