Question

I’ve been looking at this issue for too long. I suspect I’m missing something obvious because I’m overfamiliar with it.

I have a schema that suffers from a unique particle violation error. I can see why but I’ve spent too long fiddling with it to be able to step back and solve the problem.

How do I phrase this schema so that it can validate the content I need to model?

The content model looks something like:

<document>     <extract>...</extract>     <structure>...</structure>     <structure>...</structure> </document> 

OR

<document>     <structure>...</structure>     <structure>...</structure> </document> 

OR

<document>     <extract>...</extract>     <extract>...</extract> </document> 

That is a document element can contain either one or more extract elements or one or more structure elements or it can contain a single extract element followed by one or more structure elements.

I have an (incorrect) schema that looks like:

<?xml version='1.0' encoding='UTF-8'?> <xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema'>      <xs:element name='document' type='Document'/>     <xs:complexType name='Document'>         <xs:choice>             <xs:sequence>                 <xs:element ref='extract' minOccurs='0'/>                 <xs:element ref='structure' minOccurs='1' maxOccurs='unbounded'/>             </xs:sequence>             <xs:element maxOccurs='unbounded' ref='extract'/>         </xs:choice>     </xs:complexType>      <xs:element name='extract' type='xs:string'/>     <xs:element name='structure' type='xs:string'/>  </xs:schema> 

(This is a stripped down verision of a much more complex schema).

cheers

nic

Answer 1

So you need a DTD-style content model of:

extract+|structure+|extract,structure+ 

The issue here being that the presence of an extract doesn’t determine which branch is being taken. But we can rewrite the content model like this:

extract,(structure+|extract*)|structure+ 

You can see this is the same if you ‘expand out’ the inner choice as if this was algebra:

extract,structure+|extract,extract*|structure+ extract,structure+|extract+|structure+     [[ extract,extract* === extract+ ]] 

And this content model can be translated back to XSD:

<xs:complexType name='Document'>  <xs:choice>   <xs:sequence>    <xs:element ref='extract'/>    <xs:choice>     <xs:element ref='structure' maxOccurs='unbounded'/>     <xs:element ref='extract' minOccurs='0' maxOccurs='unbounded'/>    </xs:choice>   </xs:sequence>   <xs:element ref='structure' maxOccurs='unbounded'/>  </xs:choice> </xs:complexType>