Major Description
I have a schema which has a padding field that can have between 0 and 5 bits in it.
The number of padding bits is controlled by an external variable which defaults to 2.
If I set it to 0 bits, I get an error:
Runtime Schema Definition Error: Expression Evaluation Error: Element {}spare does not have a value.
That comes from this definition:
<xs:element name="spare" type="vmfgi:padding" dfdl:length="{ $l16common:l16WordPaddingBits }"/>
The type vmfgi:padding has an assert that checks that the padding field contains the value 0.
<xs:simpleType name="padding" dfdl:lengthKind="explicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:assert test="{ . eq 0 }" /> </xs:appinfo> </xs:annotation> <xs:restriction base="xs:unsignedInt"> <xs:enumeration value="0" /> </xs:restriction> </xs:simpleType>
Arguably, there shouldn't be an assert here. Just the restriction that it is 0 valued.
But ignoring that for a minute. If I did need this padding element to have a value, it will get a value if there are any bits parsed, but it has no value at all if the length is zero bits.
That requires me to model these spare fields as a complex type so that I can have a choice between no spare field, and having one, based on the padding bits value being 0 or greater than zero.
I could do that. But arguably, a zero-bit-long integer should have value 0 shouldn't it? That certainly would simplify things.
I have requested a clarification from the DFDL Workgroup. However, a runtime SDE for this clearly seems wrong. The failure should be either a parse error because zero bits is not a legal representation, or there should be no error and the integer value should be 0.