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RE: constraints on model group schema components: Unique Particle Att ribution

From: Kriegesmann, Peter <Peter.Kriegesmann@softwareag.com>
Date: Mon, 25 Mar 2002 19:21:47 +0100
Message-ID: <DFF2AC9E3583D511A21F0008C7E62106023722E7@daemsg02.software-ag.de>
To: "'noah_mendelsohn@us.ibm.com'" <noah_mendelsohn@us.ibm.com>
Cc: "'xmlschema-dev@w3.org'" <xmlschema-dev@w3.org>
Thank you very much for your help Noah.
This was exactly the information I needed.

In fact I thought an "intelligent" parser might scan further particles and
let the document pass, if there are only element references.

But this is a violation against 

http://www.w3.org/TR/xmlschema-1/#coss-modelGroup

3.8.6 Constraints on Model Group Schema Components

Schema Component Constraint: Unique Particle Attribution 

the particle contained .... can be uniquely determined without examining the
content or attributes of that item, and without any information about the
items in the remainder of the sequence. 

So you are right,

Thank you very much,

Peter

-----Original Message-----
From: noah_mendelsohn@us.ibm.com [mailto:noah_mendelsohn@us.ibm.com]
Sent: Montag, 25. Marz 2002 18:47
To: Kriegesmann, Peter
Cc: xmlschema-dev@w3.org
Subject: Re: constraints on model group schema components: Unique
Particle Att ribution


In your example, the fragment:

<xs:element name = "child">
    <xs:complexType>
      <xs:sequence>
        <xs:element ref = "x" minOccurs = "0"></xs:element>
        <xs:element ref = "x" minOccurs = "0"></xs:element>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

violates the unique article attribution constraint.  Reason: when 
validating the instance

<child>
        <x/>
</child>

you don't know whether the <x/> matches the first for the second reference 
to x.    If you look at the specification at [1] you will see that the 
declaration of the sequence turns into a list of two particles.  The fact 
that both particles reference the same declaration as their {term} [2] 
does not result in the two particles being combined.  There are two 
particles and thus an ambiguity.

[1] http://www.w3.org/TR/xmlschema-1/#Model_Group_details
[2] http://www.w3.org/TR/xmlschema-1/#cParticles
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Noah Mendelsohn                              Voice: 1-617-693-4036
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Received on Monday, 25 March 2002 13:22:04 GMT

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