Reading the spec sections 7 and 8, it does not explicitly state that at most one 'format' annotation can appear at an annotation point. But I think I know why. Firstly, we used to have selectors in the spec, which would have allowed multiple 'format' annotations on the same object, although looking back to draft 035 of the spec, the wording for selectors makes it clear that it allowed just one annotation to be chosen from the set of annotations. Secondly, we used to allow multiple formats on certain objects - remember the "applies" attribute, which had values "toScope" and "hereOnly". When both these features were dropped I think the wording in the spec was not updated to say that at most one 'format' annotation can appear at an annotation point. There used to be an example that showed two dfdl:formats in a dfdl:defineFormat - that was changed to show just one.

Thinking about it, the IBM DFDL xsd for DFDL annotations can't impose the one annotation constraint, as it only supplies global elements for dfdl:element etc. So that check must be being imposed by IBM DFDL code.

However the IBM DFDL xsd allows multiple dfdl:format within dfdl:defineFormat, but again IBM DFDL code issues an error if more than one is found. I think this is a hangover from selector support and should be corrected in the xsd. (The IBM code was originally written when selectors were in the spec.)

<xsd:element name="defineFormat" type="dfdl:DFDLDefineFormat" />
<xsd:complexType name="DFDLDefineFormat">
<xsd:sequence>
<xsd:element maxOccurs="unbounded" minOccurs="0"
ref="dfdl:format" />
</xsd:sequence>
<xsd:attribute name="name" type="xsd:NCName" />
<xsd:attribute ref="ibmDfdlExtn:basicProperties" />
</xsd:complexType>

I strongly feel that the only time we should allow multiple 'format' annotations at the same annotation point is if we add support for selectors in a future DFDL version.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: Steve Hanson/UK/IBM@IBMGB,
Cc: dfdl-wg@ogf.org
Date: 30/10/2012 19:00
Subject: Re: [DFDL-WG] question relevant to evaluation timing - short form

But, do you know where in the spec or the errata there are any constraints on format annotations at a particular annotation point? I'm aware of the one about discriminators (only one, and excludes asserts). But I can't find anything saying that you can't have more than one format annotation at a given annotation point, nor anything constraining the relative order of the various annotations that appear at a given annotation point that would dis-allow inter-leaving them arbitrarily. (Though I'm happy to see this constrained.)

I also can't find anything in the IBM XML Schema for DFDL annotations that would constrain this. This describes the properties allowed on individual annotation elements, but I don't see how it constrains how they are combined/interleaved.

On Tue, Oct 30, 2012 at 2:32 PM, Steve Hanson <smh@uk.ibm.com> wrote:
This makes no sense to me. It doesn't work - you can't spread properties across multiple annotations and expect the timing to be different at runtime - what if dfdl:length was on one and dfdl:lengthKind on the other?

IBM DFDL disallows this in its xsd for DFDL annotations. Spec should make this clear if it doesn't already.

Regards

Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh@uk.ibm.com
tel:+44-1962-815848

From: Mike Beckerle <mbeckerle.dfdl@gmail.com>
To: dfdl-wg@ogf.org,
Date: 30/10/2012 17:50
Subject: [DFDL-WG] question relevant to evaluation timing - short form
Sent by: dfdl-wg-bounces@ogf.org

Can I do this?

<sequence>
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>
    </appinfo></annotation>
</element>

See how I am spreading out the evaluation of the runtime-valued properties with the setVariable and newVariable stuff.

This works so long as we evaluate everything in schema definition order.

Now let me throw one more wrench (spanner for the UK folks) in the works. I'm going to add a short form annotation:

<sequence dfdl:separator="{... expression...}">
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>
    </appinfo></annotation>
</element>

Now, a short form annotation is equivalent to a long form conversion thereof, but in this case is it this one???

<sequence>
   <annotation><appinfo...>
     
      <dfdl:sequence separator="{...expression ...}"/> 

      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>

    </appinfo></annotation>
</element>

Or... is it this one:

<sequence>
   <annotation><appinfo...>
      <dfdl:setVariable ref="foo" .../>
      <dfdl:sequence initiator="{...expression involving foo...}"/>
      <dfdl:newVariableInstance ref="foo" value="{...some expression...}"/>
      <dfdl:sequence terminator="{...expression involving foo...}"/>

      
      <dfdl:sequence separator="{...expression ...}"/> 
    </appinfo></annotation>
</element>

I would argue I prefer the first one, because makes the lexical order of appearance consistent with evaluation order.

...mikeb

--
Mike Beckerle | OGF DFDL WG Co-Chair
Tel: 781-330-0412
-- dfdl-wg mailing list dfdl-wg@ogf.org https://www.ogf.org/mailman/listinfo/dfdl-wg

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU

--
Mike Beckerle | OGF DFDL WG Co-Chair
Tel: 781-330-0412

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU