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
