I have a long-standing concern about the usability of dfdl:lengthKind,
which others in IBM are encountering when modeling real life formats such
as EDI.
My main concern is below. For example, what's the semantic of setting
different values on the element and the sequence?
<xs:element name="container" dfdl:lengthKind="implicit">
<xs:complexType>
<xs:sequence dfdl:separator="@" dfdl:lengthKind="implicit">
<xs:element name="one" type="xs:string" dfdl:lengthKind="delimited"
/>
<xs:element name="two" type="xs:string" dfdl:lengthKind="delimited"
/>
<xs:element name="three" type="xs:string"
dfdl:lengthKind="delimited" />
</xs:sequence>
</xs:complexType>
</xs:element>
It gets even more noticeable if I set a scoping dfdl:lengthKind on the
complex type.
I propose that we limit dfdl:lengthKind to elements only. It means that
the length of a xs:sequence or xs:choice is always and implicitly given by
its chidren, and if you want to provide an explicit length or a length
prefix you must use a complex element to wrap the sequence or choice. We
have looked at the implications on dfdl:choiceKind for choices, and
dfdl:occursKind on arrays, and the proposal works happily in those
scenarios.
There's an analogy here with not alowing sequences and choices to repeat,
only elements.
It also simplifies the grammar, in the sense that any excess fill
characters in a 'box' are always considered part of the element when
parsing.
I'd like to discuss this on today's call.
Regards
Steve Hanson
Programming Model Architect
WebSphere Message Brokers
Hursley, UK
Internet: smh(a)uk.ibm.com
Phone (+44)/(0) 1962-815848
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