XML DTD Syntax - A burning question

W. Eliot Kimber eliot at isogen.com
Mon Mar 30 20:00:57 BST 1998

At 06:45 PM 3/30/98 +0100, Paul Foster wrote:
>The '*' character following an  element name implies that the element
>can occur zero or more times, '+' indicates it can occur one or more
>times.  But, what happens in the unlikely event that I want to specify
>that the element occurs exactly 50 times, or upto 50 times.  Is there a
>short cut way of doing it or do I have to write the element name out 50

Yes, you have to write it out 50 times. The ability to specify a numeric
occurrence indicator has long been discussed as something to add as part of
the SGML revision. 

Of course, it's easy to write a validation program that simply counts the
number of occurrences to see if they exceed 50. 

When thinking about these issues, it's important to keep in mind that no
matter how much DTD syntax is extended, or how much funtionality you put
into some other schema language, for non-trivial uses of XML, there will
almost always be things that need to be validated that can only be
validated by specialized processors.

Thus, you can expect to always have to write some form of "validation
application" to do whatever validation you don't get for free from your
parser or schema-specific processor. Given that, the cost of adding frills
like numeric occurrence to SGML or XML may outweigh the general benefit.
Revising standards has a very high cost, both in terms of the time of the
people who do it and the potential for breakage.


<Address HyTime=bibloc>
W. Eliot Kimber, Senior Consulting SGML Engineer
Highland Consulting, a division of ISOGEN International Corp.
2200 N. Lamar St., Suite 230, Dallas, TX 95202.  214.953.0004

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