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RE: Optional elements and restrictions

• To: "Pete Cordell" <petexmldev@t...>,<xml-dev@l...>
• Subject: RE: Optional elements and restrictions
• From: "Lawson, Marc" <mlawson@r...>
• Date: Thu, 10 Nov 2005 13:33:44 -0500
• Thread-index: AcXmJOcMUlkmTwHWR/GlW+/lQGlbdQAAFKNg
• Thread-topic: Optional elements and restrictions

Thanks, Pete.  This is very helpful.

-----Original Message-----
From: Pete Cordell [mailto:petexmldev@t...] 
Sent: Thursday, November 10, 2005 1:30 PM
To: Lawson, Marc; xml-dev@l...
Subject: Re:  Optional elements and restrictions

Hi Marc,

The behaviour you describe is correct.  As you know, 
<DESTINATION_SYSTEM_ID/> is equivalent to
<DESTINATION_SYSTEM_ID></DESTINATION_SYSTEM_ID> and none of the
specified 
enumerations match "".

I personally don't see how an "empty element" can be considered
equivalent 
to an "omitted element",  (e.g. consider <br /> in (early) (X)HTML), so 
changing the data source seems the correct thing.  If reality does not
allow 
that, you could add an additional enumeration of the form:

<xs:enumeration value=""/>

But that would probably require additional application layer processing
to 
fix it up!

HTH,

Pete.
--
=============================================
Pete Cordell
for XML to C++ data binding visit
http://www.tech-know-ware.com/lmx
=============================================

----- Original Message ----- 
From: "Lawson, Marc" <mlawson@r...>
To: <xml-dev@l...>
Sent: Thursday, November 10, 2005 5:47 PM
Subject:  Optional elements and restrictions


Hi,

In my schema, I have an "optional" element that looks like this:

<xs:element name="DESTINATION_SYSTEM_ID" minOccurs="0">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="TRUST_PROD"/>
<xs:enumeration value="TRUST_TEST"/>
<xs:enumeration value="PENSION_PROD"/>
<xs:enumeration value="PENSION_TEST"/>
</xs:restriction>
</xs:simpleType>
</xs:element>


My instance document will fail validation if the element is provided
without any data, as in...

<DESTINATION_SYSTEM_ID/>

However, the instance document will pass validation if the element is
omitted altogether.

I am hearing that it is best practice to allow both scenarios - the
"empty element" and the "omitted element" - in documents that are
provided.  Do I need to tell the company that is sending the file to
omit the element if it doesn't have data, or can I restructure the
schema to only validate elements that have data?

Any input is appreciated!
Marc Lawson

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