[DFDL-WG] clarification needed: assert evaluation order and arrays

[Steve Hanson]

You can't do that with one assert I'm afraid. The main issue is that a 
path location must always return exactly one item, so it's use within the 
context of an array must be in conjunction with a predicate, which must 
refer to a single instance.  That's what dfdl:occursIndex() is for.

To check that an array meets its bounds, you need a separate assert that 
uses the dfdl:count() function. You'd have to hard-code the min/max 
values, and place it on a containing object.

<sequence>
   <annotation><appinfo...>
      <dfdl:assert>{ dfdl:occursCount(./foo) ge 5 and 
dfdl:occursCount(./foo) le 10 }</dfdl:assert>
   </appinfo></annotation>
   <element name="foo" minOccurs="5" maxOccurs="10" 
dfdl:occursCountKind='parsed'>
     <annotation><appinfo...>
      <dfdl:assert>{ dfdl:checkConstraints(.[dfdl:occursIndex()]) 
}</dfdl:assert>
     </appinfo></annotation>
     <simpleType>
       <restriction base="xs:string">
        <pattern value="...some regex..."/>
       </restriction>
     </simpleType>
  </element>
</sequence>

I think that means our definition of dfdl:checkConstraints() in the spec 
is wrong. Table 34 and Section 5.2 together imply that minOccurs and 
maxOccurs are used in checkConstraints. I think that simply doesn't work. 
It should only be using 'fixed' and the facets (I think 'default' is 
pointless as well).

Worth noting that when a path is used in the context 
dfdl:occursCount(<path>) then it is not an error if more than one item is 
returned, and it should not be wrapped with fn:exactly-one().

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     dfdl-wg at ogf.org, 
Date:   01/11/2012 16:45
Subject:        [DFDL-WG] clarification needed: assert evaluation order 
and arrays
Sent by:        dfdl-wg-bounces at ogf.org




Question: If I write 

<element name="foo" minOccurs="5" maxOccurs="10" 
dfdl:occursCountKind='parsed'>
   <annotation><appinfo...>
      <dfdl:assert>{ dfdl:checkConstraints(.) }</dfdl:assert>
   </appinfo></annotation>
   <simpleType>
     <restriction base="xs:string">
        <pattern value="...some regex..."/>
     </restriction>
   </simpleType>
</element>

I have two sources of constraints. One is the pattern, the other the 
min/max occurs.

Does that one assertion calling dfdl:checkConstraints mean both will be 
checked? 
That is, one check occurring as each element is parsed, and the other at 
the end of the array?

Assume I am not using any validation option, so the DFDL processor would 
not otherwise check the max/minOccurs because occursCountKind is parsed.

Will the checkConstraints fail as soon as we parse the 11th element (is it 
checking the min/max occurs for each element occurrence as it is parsed), 
or do we parse as many as we can, and fail only when we check and find out 
that the entire array has 36 elements that were successfully parsed? 

What I would like the above to mean is this:

1) as each element occurrence is parsed we check the pattern and parse 
error (assertion failed) if there is no match. 
2) Also after a successful parse of an occurrence, we check that the index 
is <=10, and parse-error (assertion failed) if not.
3) at the end of the array, we check that the number of occurrences is >= 
5. If not we get a parse error (assertion failed). 

Comments?





...mikeb

-- 
Mike Beckerle | OGF DFDL WG Co-Chair 
Tel:  781-330-0412
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