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RE: [xml-dev] What does "optional" mean?

The answer can be very simple. For example, I work in drug information.
We have a standard section dealing with drug abuse/dependency, which is
a vitally important section *when it applies*. However, many drugs are
not problematic in this regard and the element is not necessary in those
instances. Therefore, it is an optional element for a drug monograph.

Honestly, I've yet to see a DTD/Schema that did not contain optional
elements, all of them important, but only within their intended context
as described above.

To answer your revised question within the context of drug information,
there are elements (e.g., Indications, Adverse Reactions) that are
always mandatory in our monographs, but other elements (a variety of
warnings and precautions) that, while common enough and important enough
to warrant a "named" element, are not relevant to every single drug
monograph and are therefore optional.

Another good example would be Black Box Warnings. This is potentially
life-or-death information, but is optional because many drugs do not
have them.

-----Original Message-----
From: Costello, Roger L. [mailto:costello@mitre.org] 
Sent: Sunday, February 26, 2012 10:16 AM
To: xml-dev@lists.xml.org
Subject: RE: [xml-dev] What does "optional" mean?

> I would agree with David Carlisle.
> In schema,  "optional" doesn't mean ANY of the items you suggest.

Yes, I stand corrected. Despite my best efforts, how quickly and easily
I fall into the trap of ascribing meaning to constructs in schemas.

Let me rephrase my question: 

       Why make one element mandatory 
      and another optional?

That is, what is it about some information that it is declared mandatory
whereas another information is declared optional?



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