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RE: What does "optional" mean?

  • From: David Lee <dlee@calldei.com>
  • To: David Carlisle <davidc@nag.co.uk>, "Costello, Roger L."<costello@m...>
  • Date: Sun, 26 Feb 2012 15:10:52 +0000

RE:  What does "optional" mean?
I would agree with David Carlisle.
In schema,  "optional" doesn't mean ANY of the items you suggest.
Schemas say nothing about "meaning".   Schemas defines syntax validity and type information.
Neither of these imply anything about "what does it mean?"

<side joke>
There's an old comic book series from the 60's 'underground'  ... "Mr. Natural".
Mr. Natural was a long haired white robed "guru" kind of guy which some of the locals followed around.
In one scene, the main local was whining and complaining about life, with questions like "Why do we have war" , "Why do bad things happen to good people"  ... all your typical religious/metaphysical questions ...  finally asked "Mr. Natural...  What does it all MEAN !!!???"

"It don't mean Shiite".

David A. Lee

> -----Original Message-----
> From: David Carlisle [mailto:davidc@nag.co.uk]
> Sent: Sunday, February 26, 2012 9:32 AM
> To: Costello, Roger L.
> Cc: xml-dev@lists.xml.org
> Subject: Re:  What does "optional" mean?
> On 26/02/2012 14:11, Costello, Roger L. wrote:
> > Every schema language (DTD, XSD, RNG) has the notion of optional --
> optional elements and optional attributes.
> XML DTD does not.
> In DTD attributes may be #IMPLIED or #FIXED and may have a default
> value, any of these declarations might colloquially be called declaring
> the attribute to be optional, but they have precise meanings given in
> the xml spec, so you don't have to worry about what optional means.
>  > I've listed three possible meanings of "optional":
>  >     -- In the first meaning, it indicates:  of-lesser-importance.
>  >     -- In the second meaning, it indicates:  irrelevance.
>  >     -- In the third meaning, it indicates:  lack-of-knowledge.
>  > So what does "optional" really mean?
> in Relax NG (and XSD, probably, but I try to avoid thinking about that)
> It doesn't mean any of those things. It just means (for attributes) that
> the attribute may be omitted from an instance.
> so if the bar attribute is declared with "?" then
> <foo> and <foo bar="">
> are both valid. There is no indication of the _meaning_  implied by
> omitting an attribute, just as there is no indication of the meaning
> implied by any particular element name.
> the role of the schema is just to say what syntax is or is not valid, it
> doesn't say anything about when or why you should use any of the syntax
> options that are valid.
> David
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