I created a JIRA ticket for this experimental feature to lift the dfdl:nilValues='%ES;' only restriction on complex type elements.
https://issues.apache.org/jira/browse/DAFFODIL-2597 On Thu, Dec 2, 2021 at 10:58 AM Mike Beckerle <mbecke...@apache.org> wrote: > It is not possible for DFDL v1.0 to lift this restriction as an erratum. > > We can explore removing it for DFDL v2.0 in the future, and create a > Daffodil experimental feature to implement this. > > The process works that way, implement/prototype the change, then with > experience from an implementation, propose it for the standard. > > In general, in DFDL, you do not get to design "the XML you want", and then > use DFDL to populate it. It simply doesn't work that way. Often tiers of > elements are required where one is not desired strictly speaking in the > model. > > The way I have seen this sort of thing modeled is like so: > > <myElement> > <nil/> > <myElement> > > <myElement> > <subElement1>....</subElement1> > <subElement2>....</subElement2> > .... > <myElement> > > So that you always have myElement at the top to identify the thing. Then > you either have child element content, or a reserved element to indicate > the nil/nulled status. > > Arguably, <myElement xsi:nil="true"/>, should be possible vs. > <myElement><nil/></myElement>. > > Another alternative is to use the lack of an element to indicate that the > element is nil. > > <choice> > <sequence dfdl:initiator="-"/> > <element name="myElement" ....> > ... complex type here... > </element> > </choice> > > Then, if the "-" is found, there will be no element at all in the infoset. > When unparsing, this choice will default to the first branch and output the > "-". > > > > > > > > On Thu, Dec 2, 2021 at 8:00 AM Roger L Costello <coste...@mitre.org> > wrote: > >> Hi Mike, >> >> >> >> 1. Would you get the DFDL committee to remove this restriction, please? >> >> >> >> 2. I have 350 data formats, each having dozens of fields with nillable >> complexTypes. So there is a strong use case for removing the restriction. >> >> >> >> 3. The choice idea that you presented, although clever and interesting, >> is not suitable. In the example I presented, the output XML should be one >> of these: >> >> >> >> <MyField>-</MyField> >> >> >> >> <MyField> >> >> <DateTimeIso>…</DateTimeIso> >> >> </MyField> >> >> >> >> <MyField> >> >> <MonthName>…</MonthName> >> >> </MyField> >> >> >> >> With the technique you showed, the output would be one of these: >> >> >> >> <noValue>-</noValue> >> >> >> >> <MyField> >> >> <DateTimeIso>…</DateTimeIso> >> >> </MyField> >> >> >> >> <MyField> >> >> <MonthName>…</MonthName> >> >> </MyField> >> >> >> >> That first one -- <noValue> -- is not unacceptable to my community. >> >> >> >> /Roger >> >> >> >> *From:* Mike Beckerle <mbecke...@apache.org> >> *Sent:* Wednesday, December 1, 2021 4:06 PM >> *To:* users@daffodil.apache.org >> *Subject:* [EXT] Re: Huh? Nillable complex type elements can only have >> '%ES;' as their dfdl:nilValue property >> >> >> >> This is definitely a DFDL language restriction, not a Daffodil-specific >> thing. >> >> >> >> I have made inquiries as to what the rationale is for this restriction, >> and I'll report back. >> >> >> >> In the mean time, maybe this sort of technique. >> >> >> >> <choice> >> >> <element name="noValue" type="xs:string" dfdl:lengthKind="explicit" >> dfdl:length="0" dfdl:initiator="-"/> >> >> <element name="myComplexType"> >> >> .... non nillable complex type definition .... >> >> </element> >> >> </choice> >> >> >> >> I have to admit that this workaround sort of suggests that there isn't a >> coherent rationale for the restriction, as this is pretty obviously >> equivalent to the complex type being nillable with nilValue="-". >> >> >> >> >> >> On Wed, Dec 1, 2021 at 12:43 PM Roger L Costello <coste...@mitre.org> >> wrote: >> >> Hi Folks, >> >> I am creating a DFDL schema for a data format that has a field whose >> value is a hyphen when no data is available and when data is available, >> then the field contains either an ISO datetime or a 3-letter month name. >> Here's how I specified the field: >> >> <xs:element name="MyField" nillable="true" dfdl:nilValue="-"> >> <xs:complexType> >> <xs:choice dfdl:choiceLengthKind="implicit"> >> <xs:element name="DateTimeIso"> >> <xs:complexType> >> <xs:sequence> >> ... >> </xs:sequence> >> </xs:complexType> >> </xs:element> >> <xs:element name="MonthName" type="xs:string" >> dfdl:length="3" dfdl:lengthKind="explicit" /> >> </xs:choice> >> </xs:complexType> >> </xs:element> >> >> When I run it, Daffodil gives this error message: >> >> [error] Schema Definition Error: Nillable complex type elements can only >> have '%ES;' as their dfdl:nilValue property. >> >> Is that an error in Daffodil? Or, is it an actual DFDL restriction? If >> the latter, why is there such a restriction? How do I work around this >> error? >> >> /Roger >> >>
