XML-Data, "&" and inheritance

Rick Jelliffe ricko at allette.com.au
Mon Apr 27 20:51:50 BST 1998

From: Paul Prescod <papresco at technologist.com>

>In reviewing XML Data for another project, I note that the XML Data
>"subclass" mechanism depends on the XML-Data equivalent of the ampersand
>operator that was removed from XML. I'm not convinced that putting that
>operator back in was a good idea. It was left ouf of XML because it
>complicates implementation.

The ampersand operator also complicates processing, if you use some stream
processing language like Perl. It means that all the contents of the element
have to be read into memory, in the worst case, before they can be
The programmer cannot rely on the sequence of the input elements.

So developers who are serializing their databases are probably much
better off to use fixed sequences (i.e.,  "," in XML content models) anyway,
if they want their data to be processed by text processing applications.

But I think XML-data (or any successor) should be free to have any
to XML or SGML markup declarations.  The more extras that XML-data (or
whatever it becomes) can provide, the more reason to justify it.

But I would hope that any W3C XML-schema proposal, perhaps reconciling
XML-data, RDF-schema and XML markup declarations, would include
definite rules for translating between element type definitions using
* current markup declaration syntax,
* element syntax, for hypertexted declarations, and
* PIs, for arbitrary inline declarations.

Also, I cannot see why XML-data does not use regular expression syntax
for specifying content models. I can see many good reasons for using
elements for defining types, but not for using elements for each part of
a content model. I note that the OmniMark program SGML2DTD, which
converts DTDs into a form quite similar to XML-data converts a
certain company's (XXX)  version of DOCBOOK DTD from 178K to
about 600K. This seems an enormous overhead. If this is so, then
XML-data schemas (as they are now) are really only suitable for smaller
DTDs (i.e, those belonging to databases), for web use.

In any case, a W3C XML-schema proposal should have clear mappings
for converting to and from XML declarations. This will make more explicit
all the wonderful benefits being gained.

Rick Jelliffe

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