RE: [xml-dev] Schema (XSD) rule precedence

["Michael Kay" <mike@saxonica.com>]

If you replaced "all" with "sequence", then you would be describing the
grammar

(a, b, c, d)?

and if you added minOccurs=0 to c, the grammar would be

(a, b, c?, d)?

It's no different with "all". For example if the outer level is optional and
the c is optional, then the grammar is

(a & b & c? & d)?

Or in English: the content can be empty, but if it is present then it must
contain exactly one a, exactly one b, an optional c, and exactly one d,
which can appear in any order.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay 


> -----Original Message-----
> From: Adam Flinton [mailto:adam.flinton@nhs.net] 
> Sent: 11 June 2009 12:48
> To: xml-dev@lists.xml.org
> Subject: [xml-dev] Schema (XSD) rule precedence
> 
> Dear All,
> 
> If I have a container element such as :
> 
>             <xs:all minOccurs="0">
>                 <xs:element ref="a" />
>                 <xs:element ref="b" />
>                 <xs:element ref="c" />
>                 <xs:element ref="d" />
>             </xs:all>
> 
> 
> And then a given element in the container has a minOccurs e.g.
> 
>   <xs:element minOccurs="1" name="a"/>
> 
> If I am walking a schema creating all required elements, do I 
> create an element <a/> or not?
> 
> i.e. what is the rule on constraints (e.g. required vs 
> optional) in a hierarchy?
> 
> TIA
> 
> Adam
> 
> 
> 
> 
> 
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