I guess I really don't see the need for the restriction.

We do need a restriction for complex types that nilKind must be 'literalValue' or 'literalCharacter', not 'logicalValue' because there are no logical values for complex types. But literalValue and literalCharacter are representational. They're not about the value of an element.

The representation of the complex type can be nilled with a nil representation of "-" without introducing any concept of "value" for the complex type element. Processing always proceeds to check the nil representation first, before checking anything else, and has to even now, given that we do allow %ES; as nil value for a complex type element.

Did this %ES; only policy stem from the fact that we didn't really understand (early on) that nilled is an orthogonal non-value flag in the infoset elements?

The fact that the workaround is this:

.... non nillable complex type definition ....

</element>

</choice>

essentially this argues that the nil representation can be checked for first, and there's no real reason why the element of complex type can't be nillable with nilValue "-".

On Wed, Dec 1, 2021 at 4:39 PM Steve Hanson <smh@uk.ibm.com> wrote:

See spec section 13.15. "to avoid the concept of a complex element having a value, which does not exist in DFDL". The parser would not know to treat the '-' as the nil value for the complex element, or the content of the first child? Allowing just %ES; avoids that.

Regards

Steve Hanson
IBM Hybrid Integration, Hursley, UK
Architect, IBM DFDL
Co-Chair, OGF DFDL Working Group
smh@uk.ibm.com
tel:+44-1962-815848
mob:+44-7717-378890
Note: I work Tuesday to Friday

From: "Mike Beckerle" <mbeckerle.dfdl@gmail.com>
To: "DFDL-WG" <dfdl-wg@ogf.org>
Date: 01/12/2021 21:07
Subject: [EXTERNAL] [DFDL-WG] What is Rationale why Nillable complex type elements can only have '%ES; ' as their dfdl:nilValue property
Sent by: "dfdl-wg" <dfdl-wg-bounces@ogf.org>

DFDL has this seemingly ad-hoc restriction.

Users naturally want to model a complex element where "-" (dash) means the whole complex element is nilled, and if not "-" then we parse and produce a complex element.

What is the rationale for this restriction?
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