Thank you Steve!
You've provided a workaround for optional choice: omit minOccurs="0" and add
<xs:sequence/> within the choice.
Is there a workaround for optional elements in a choice?
/Roger
-----Original Message-----
From: Steve Lawrence <slawre...@apache.org>
Sent: Friday, March 25, 2022 8:07 AM
To: users@daffodil.apache.org
Subject: [EXT] Re: Recommended changes to the DFDL language
One alternative for minOccurs on a choice is to have an empty branch:
<xs:choice>
<xs:element name="foo" ... />
<xs:sequence />
</xs:choice>
I admit that minOccurs="0" is a little more self documenting.
I think minOccurs also means something different if there are delimiters on the
choice. For example, say we had these two snippets to implement an optional
choice with a terminator:
<xs:choice dfdl:terminator="X">
<xs:element name="foo" ... />
<xs:sequence />
</xs:choice>
and
<xs:choice dfdl:terminator="X" minOccurs="0">
<xs:element name="foo" ... />
</xs:choice>
In the former, if the X terminator doesn't exist, then it is a parse error. But
in the later case with minOccurs, if the X terminator doesn't exist then it
just means the choice doesn't exist.
So the semantics are a bit different. All that said, I don't think I've come
across a case where we've absolutely needed minOccurs="0" on a choice, and not
allowing it keeps DFDL simpler.
As to nillable complex other than %ES;, we have a ticket open to add this as an
experimental feature, currently slated for the next release:
https://issues.apache.org/jira/browse/DAFFODIL-2636
On 3/25/22 7:46 AM, Roger L Costello wrote:
> Hi Folks,
>
> I am converting 350 military data formats to DFDL.
>
> Everyone of the 350 data formats has an optional choice:
>
> <xs:choice minOccurs="0">
>
> DFDL does not allow optional choice. Why?
>
> I recommend changing the DFDL language to allow optional choice.
>
> Everyone of the 350 data formats has branches of a choice that are optional:
>
> <xs:choice>
> <xs:element name="foo" minOccurs="0">
>
> DFDL does not allow branches in a choice to be optional. Why?
>
> I recommend changing the DFDL language to allow optional branches of a choice.
>
> Many of the 350 data formats have an element with complexType that is
> nillable and the nilValue is a hyphen.
>
> DFDL does not allow an element with complexType to have a nilValue
> other than %ES;
>
> I recommend changing the DFDL language to allow elements with
> complexType to have a nilValue other than %ES;
>
> /Roger
