[DFDL-WG] Catch 22.for EVDP & NVDP ?

[Steve Hanson]

        <xs:element name="choiceGroup" dfdl:lengthKind="implicit">
                <xs:complexType>
                        <xs:choice dfdl:choiceLengthKind="implicit" 
dfdl:initiatedContent="yes">
                                <xs:element name="myNum1" type="xs:int" 
dfdl:lengthKind="explicit"
 dfdl:length="2"
 dfdl:textNumberPattern="#0"
 dfdl:initiator="num:"
 dfdl:terminator="~" />
                                                                 >
                                <xs:element name="myText1" 
type="xs:string" dfdl:lengthKind="explicit"
 dfdl:length="2"
 dfdl:initiator="text:"
 dfdl:terminator="~" />
                        </xs:choice>
                </xs:complexType>
        </xs:element>

The above model is a choice of two elements, each of which is fixed length 
and has an initiator and terminator. Because the elements are fixed 
length, I must set dfdl:emptyValueDelimiterPolicy (EVDP) to be 'none' **. 
I also want to discriminate using the initiator, so I set 
dfdl:initiatedContent 'yes' on the choice, so I must set EVDP to 
'initiator' or 'both' ++.  (Same for NVDP if nillable). Catch 22.

** 'none' because the only valid empty representation is that there is 
nothing there at all. The element is fixed length X, so if the delimiters 
are present then the content must be length X and can't be zero length.

++ 'initiator' or 'both' because an initiator must always be present when 
dfdl:initiatedContent 'yes'. 

The implication is that I can't use dfdl:initiatedContent for this choice. 
While I can switch off nillable to avoid the error with NVDP, there is no 
other way of avoiding the EVDP error.

Regards
 
Steve Hanson
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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