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Re: Recurring Data Types / Namespaces?

From: <Noah_Mendelsohn@lotus.com>
Date: Wed, 4 Oct 2000 10:58:04 -0400
To: "Joe Melton" <jmelton@cardinalsolutions.com>
Cc: www-xml-schema-comments@w3.org
Message-ID: <OF2633AA62.82559B7E-ON8525696E.004BAC27@lotus.com>
Joe Melton asks:

>> Is it legal for a parent node to have multiple child nodes with the 
>> same reference type? Here is an example of what I am referring to. 
>> CreditSurchargeDt and SecondaryCD occur twice in this sequence. 

 1) <group name="PCCREDITSURCHARGE">
 2)   <sequence minOccurs="0" maxOccurs="1">
 3)     <element ref="CreditSurchargeDt" minOccurs="0" maxOccurs="1"/> 
 4)     <element ref="SecondaryCd" minOccurs="0" maxOccurs="1"/> 
 5)     <element ref="CreditSurchargeDt" minOccurs="0" maxOccurs="1"/>
 6)     <element ref="DiscountSurchargeFactorCd"/>
 7)     <element ref="Amount" minOccurs="0" maxOccurs="1"/>
 8)     <element ref="IterationNumber" minOccurs="0" maxOccurs="1"/>
 9)     <element ref="SecondaryCd" minOccurs="0" maxOccurs="1"/>
10)   </sequence>
11) </group>

The general answer is yes, such multiple occurrences are legal in a 
sequence.   You may be looking for an <all> group, in which duplicates are 
not legal, sequence is not relavent to validation (though is still 
significant in the XML infoset), and optionality (minOccurs="0" 
maxOccurs="1") is allowed.

The detailed and perhaps surprising analysis of your example, if I've 
eyeballed it right is that SecondaryCD is legal, CreditSurchargeDt is not. 
 Why?  We have a constraint that content models support unambigous 
attribution during validation.  To keep the examples terse, I'll use DTD 

legal:     A,A
legal:     A,A? 
not legal: A?, A?
not legal  A?, B?, A?

Why?  Consider the instance document:


In the legal content models you always know that the <A/> matches the 
first A.  In the illegal ones it's ambiguous; the single <A/> could match 
either of the optional A?'s.  Your CreditSurchargeDt seems isomorphic to 
the last illegal model, since both its occurrences are optional and 
everything in between is optional.

legal: A?, B, A?

because if A comes before the required B, it matches the first one, 
otherwise the second.  I think this is the reason your SecondaryCD is OK, 
because you have a non-optional DiscountSurchargeFactorCd (#6) between the 
two references (#4 and #9). 

I hope I have this right, and I hope this helps.

Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
Received on Wednesday, 4 October 2000 11:02:29 UTC

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