[x3d-public] Fw: ProtoInstance USE without name

[Andreas Plesch]

On Sat, Dec 5, 2020 at 6:33 PM Don Brutzman <brutzman at nps.edu> wrote:

> On 12/5/2020 2:41 PM, Andreas Plesch wrote:
> > [...]
> >     Assuming X3D4 completion and acceptance, in a few months when we get
> to revision of X3D XML Encoding 19776-1 we can consider special wording for
> ProtoInstance if it survives further scrutiny and consensus emerges on
> merit.  For today, as usual, X3D Schematron is following strict
> interpretation of specification:
> >
> >     * X3D XML encoding > 4 Concepts > 4.3.4 DEF and USE attribute syntax
> >
> https://www.web3d.org/documents/specifications/19776-1/V3.3/Part01/concepts.html#DEFAndUSEAttributeSyntax
> <
> https://www.web3d.org/documents/specifications/19776-1/V3.3/Part01/concepts.html#DEFAndUSEAttributeSyntax
> >
> >
> >     'Nodes containing a USE="someName" attribute can include no other
> attributes except containerField and class. Default values for other fields
> shall be ignored since field definitions in the original DEF node
> declaration have precedence.'
> >
> > 'Nodes' seems to refer to X3D nodes but may be intended to refer to XML
> nodes. To avoid ambiguity, consider specifying 'XML elements' instead. I
> think strictly speaking attributes are also nodes in XML
> >
> > With such a change ProtoInstance would fall under that requirement.
>
> In general: 19775-1 X3D Architecture refers to X3D nodes, while 19776-2
> X3D XML encoding refers to XML elements representing those same X3D nodes.
>



>
> So the quoted 'Nodes' above is X3D node and also XML element.
>

Yes. This is a section from the XML encoding (19776-1). In the preceding
text "nodes" is used to refer to X3D nodes. The confusion, for me, comes
from the fact that ProtoInstance is not a X3D node by itself.


> I don't think we want the abstract Architecture to say anything about XML,
> but to continue to strive for an Architecture that has fully representable
> functionality in each of the subsidiary file encoding (19776-*) and
> programming language bindings (19777-*) standards.
>

Agreed, this is only about the XML encoding.


>
> This all requires careful phrasing!  In case anyone isn't wary yet,
> XML-speak (and DOM) often refers to XML elements as document nodes, as well.
>

DOM language, in particular, prefers "node".


> It is a little bit of a chore when programming a parser with ProtoInstance
> USE support to look up the name of the original DEF ProtoInstance, but
> knowing that consistency is correct in a scene is certainly helpful.
>

And most browsers ( including x3dom, but not all ) do not require the name
attribute with USE. So that is ok. The problem is only that the spec. is
not clear if the name is required or not. The tooltips (and the validation
tools due to technical constraints) do not require it and actually forbid
it but the spec. language itself is just not conclusive. If no attribute
would be allowed with USE ( as is the case with XML elements which are x3d
nodes ), name cannot be required.


> And so, still thinking our current state of affairs to have XML models
> with a ProtoInstance USE not require a name (while clearly erroneous if an
> included name mismatches) seems OK and provides round-trippable correct
> results.  This pattern also played out satisfactorily in the JSON encoding,
> Java X3DJSAIL and Python x3d.py without mishap.
>

I agree. It would be reasonable that name should not be required. But the
spec. currently allows browsers to require it, as far as I can tell.

https://savage.nps.edu/X3dValidator/ does not seem to work currently, eg.
the Validate button stays greyed out ?

all the best, -Andreas


> all the best, Don
> --
> Don Brutzman  Naval Postgraduate School, Code USW/Br
> brutzman at nps.edu
> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA   +1.831.656.2149
> X3D graphics, virtual worlds, navy robotics
> http://faculty.nps.edu/brutzman
>


-- 
Andreas Plesch
Waltham, MA 02453
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