<choice>
<element minOccurs="0" .../>
....
</choice>
Becomes
<choice>
<sequence>
<element minOccurs="0" .../>
</sequence>
....
</choice>
Now the child of the choice is a non-optional sequence element.
On Fri, Mar 25, 2022 at 8:15 AM Roger L Costello <coste...@mitre.org> wrote:
> 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
>
