RE: inquiry into the <choice> element behavior

If you had maxOccurs="1", you would be limited to a single element, which
must be a foo or a bar. But with maxOccurs="unbounded", you can have any
number of elements, each of which must be either a foo or a bar. If you
moved the maxOccurs to the xs:element elements, then you would be allowed
any number of elements so long as they are all foo elements, or all bar
elements, but not a mixture.
 
If you're familiar with BNF grammars, what you have written is
 
(foo | bar)*
 
whereas it seems you might want
 
(foo* | bar*)
 
Michael Kay


  _____  

From: xmlschema-dev-request@w3.org [mailto:xmlschema-dev-request@w3.org] On
Behalf Of Jeffrey.Kramer@dds.net
Sent: 30 October 2008 18:45
To: xmlschema-dev@w3.org
Subject: inquiry into the <choice> element behavior



We were hoping to get a definitive answer on how the <choice> element is
supposed to behave.   

We observed kind of a counter intuitive result of choice in a test.  i.e.,
we'd think it was going to be mutually exclusive across it's elements,
although when we provided >1 types it actually spit out both ( see below ) 

i.e., 

providing 
... 
        <foo>1</foo> 
        <foo>2</foo> 
        <bar>3</bar> 
.. 
to 
. 
          <xs:choice  maxOccurs="unbounded"> 
            <xs:element name="foo" type="xs:string" /> 
            <xs:element name="bar" type="xs:string" /> 
       </xs:choice> 

yields: 
        
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #startElement: foo

2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #characters: 1 
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #endElement: foo 
        
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #startElement: foo

2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #characters: 2 
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #endElement: foo 
        
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #startElement: bar

2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #characters: 3 
2008-10-30 11:55:17,726 main DEBUG xml.UnmarshalHandler - #endElement: bar 


We were kind of thinking the choice would somehow be limited to only one of
nested elements.  Perhaps we're misusing the maxOccurs?   Any insights
greatly appreciated.  Thanks in advance. 

- Jeff