[DFDL-WG] Unparser maxOccurs issue

12 Jan 2015

      Possible change to spec needed., where it describes what happens when 
maxOccurs is exceeded during unparsing for occursCountKind 'fixed' and 
'implicit' (and by implication scalar elements). 

It currently says it is a processing error. I think it is better to say 
that the unparser moves on when maxOccurs is reached. This makes the 
behaviour analogous to parsing, when it does not try to parse beyond 
maxOccurs and moves on.  The current unparser wording is based on the 
assumption that any next occurrence of the element in the infoset must be 
an error, but this is not true - the next occurrence could be an 
occurrence of a same named element later in the schema. 

An obvious example is:

<xs:element name="data" minOccurs="2"maxOccurs="2" 
dfdl:occursCountKind="fixed" ... /> 
<xs:element name="stuff" minOccurs="0" dfdl:occursCountKind="implicit" ... 
/> 
<xs:element name="data" maxOccurs="2" maxOccurs="2" 
dfdl:occursCountKind="fixed" ... /> 

with an infoset where 'stuff' is missing:

message_data
  data - xx1
  data - xx2
  data - yy1
  data - yy2

A more interesting example is this, taken from MIL-STD-2045 schema (my 
bold comments added):

<xsd:sequence dfdl:separator="">
<!-- Element Value1 -->
        <xsd:choice>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_true"/>
            <xsd:element dfdl:length="4" dfdl:lengthKind="explicit" 
name="Value1" type="xsd:string"/>
          </xsd:sequence>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_false"/>
          </xsd:sequence>
        </xsd:choice>
<!-- Element Value2 -->
        <xsd:choice>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_true"/>
            <xsd:element dfdl:length="4" dfdl:lengthKind="explicit" 
name="Value2" type="xsd:string"/>
          </xsd:sequence>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_false"/>
          </xsd:sequence>
        </xsd:choice>
<!-- Element Value3 -->
        <xsd:choice>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_true"/>
            <xsd:element dfdl:length="4" dfdl:lengthKind="explicit" 
name="Value3" type="xsd:string"/>
          </xsd:sequence>
          <xsd:sequence dfdl:separator="">
            <xsd:group ref="FPI_false"/>
          </xsd:sequence>
        </xsd:choice>
</xsd:sequence>

...where the FPI_true and FPI_false elements are defined in their own 
global groups.

  <xsd:group name="FPI_true">
    <xsd:sequence dfdl:separator="">
      <xsd:element default="true" dfdl:length="1" 
dfdl:lengthKind="explicit" dfdl:textBooleanFalseRep="0" 
dfdl:textBooleanTrueRep="1" name="FPI_true" type="xsd:boolean">
        <xsd:annotation>
          <xsd:appinfo source="http://www.ogf.org/dfdl/">
            <dfdl:discriminator>{. eq fn:true()}</dfdl:discriminator>
          </xsd:appinfo>
        </xsd:annotation>
      </xsd:element>
    </xsd:sequence>
  </xsd:group>

  <xsd:group name="FPI_false">
    <xsd:sequence dfdl:separator="">
      <xsd:element default="false" dfdl:length="1" 
dfdl:lengthKind="explicit" dfdl:textBooleanFalseRep="0" 
dfdl:textBooleanTrueRep="1" name="FPI_false" type="xsd:boolean">
      </xsd:element>
    </xsd:sequence>
  </xsd:group>

If the infoset looked like the following an error would be given, whereas 
it is valid because the second FPI_false is for Value2:

message_prefixedOccurs
  FPI_false - false
  FPI_false - false
  FPI_true - true
  Value3 - 9999

Regards

Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848
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