[x3d-public] Validation improvements for "USE" attribute

[Don Brutzman]

Primary is getting to clarity on best possible USE definition for X3D per se.  We discussed Thursday on spec teleconference.

It would seem that allowing different 'class' attributes on USE in the XML Encoding is over-generous and should be tightened to not be allowed.  We were able to come up with examples that showed diverse class+USE is problematic (e.g. cannot style a Material node to be a class='somethingBlue' while styling a USE version of the same node to be class='somethingRed').

Next will be considering if 'class' attribute can be advanced to abstract spec and hence all encodings; currently it is only reserved/defined in XML Encoding.

Regarding DOM tree and X3D tree, they do not have to be considered as necessarily identical all of the time.  If event models are decoupled and handing off in tandem, then synchronization would occur after each respective update.  There are different ways for implementations to accomplish this - all worth considering, with HTML5/DOM Recommendations being authoritative regarding functionality.

So, step by step.  If we can define semantics that work consistently/coherently, and can be implemented, we then refine iteratively for use in each X3D encoding.



On 6/15/2017 10:58 AM, Leonard Daly wrote:
> The original purpose (and still used in this manner) of the 'USE' attribute is to indicate that another node should also appear in place of the node declaring 'USE'. In fact the specification states (4.4.3 - http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/concepts.html#DEFL_USESemantics) that "the same node is inserted into the scene graph a second time, resulting in the node having multiple parents".
> 
> This requirement is not allowed in DOM (see https://www.w3.org/TR/dom/#concept-node-tree for the standard, https://www.w3.org/wiki/Traversing_the_DOM#Nodes for the explanation). A DOM element is allowed to have at most one parent. It is possible to create a (deep) copy of the node and insert it into the tree. That gives a structure like:
> 
> [Meant to be seen in fixed width font]
> 
>    B - C - D
> /
> A
>   \
>     E -CC -DD
> 
> Where A is the parent of this (sub-)tree, B is the node that start one branch (e.g., Transform). C is the 'DEF'ed node with a child of D. E is a separate child of A (e.g., a different Transform) CC is the 'USE' version of C. Since HTML does not allow multiple parents ('B' and 'E'), a copy of 'C' needs to be made. This needs to be a deep copy (all children) as no node can have more than one parent.
> 
> The problem with a deep copy is that it is non-deterministic as the element is self-referential (it refers to it's parent, which refers to it...)
> 
> It seems to me that there is a conflict in requirements between X3D's statement on DEF/USE and the requirement to put all X3D nodes in the DOM. There are several ways around this:
> 1) Remove the multiple parent requirement from DEF/USE
> 2) Remove the requirement of all nodes being in the DOM.
> 
> Each has advantages and disadvantages. Which choice is made determines how X3D operates in the HTML/DOM environment.
> 
> 
> Leonard Daly
> 
> 
> 
> 
> 
> 
> 
>> Hi all,
>>
>> Recently we updated the DTD/schemas to make the “name” field of nodes like MetadataBoolean, or FloatVertexAttribute a required field. However, we then realised that when any of these nodes has the “USE” attribute, the “name” field must not be set. Hence the changes needed to be revisited.
>>
>> I started to look at the JSON schema for the MetadataBoolean node, to try to implement this stricter validation requirement. With some online assistance I found that I could easily make either one or the other required, but not both. This would meet the original requirement.
>>
>> However, this raised a more general question in my mind. When any node has the “USE” attribute set, what other fields/attributes are permitted?
>>
>> As a test case, I concentrated on the MetadataBoolean node. I came up with a JSON schema that might illustrate this better. I have attached a snapshot image for this fragment of the JSON schema.
>>
>> The validation of the MetadataBoolean node begins with a “one of” operator (shown immediately to the right of the MetadataBoolean box. This operator requires that one, and only one, of the two subschemas be valid. For the first subschema (the upper of the two) I simply removed the “@USE” property, making the “@name” field required (to meet the original requirement). For the second subschema (the lower of the two) I made the “@USE” property required, and only added the “IS” property. Note that both subschemas only permit those properties listed (i.e. additional properties are disallowed).
>>
>> In principle, there should be no difficulty applying this validation methodology within the JSON schema to all nodes.
>>
>> Some questions:
>>
>>  1. Is this validation methodology correctly aligned with the standards?
>>  2. Do we want to apply this methodology to all nodes?
>>  3. Do we want to apply this methodology to other validation tools, e.g. Schematron, and also consider whether the XML schema or the DTD have sufficient expressive power too.
>>
>> All comments appreciated,
>>
>> All the best,
>>
>> Roy
>>
>>
>>
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> 
> 
> -- 
> *Leonard Daly*
> 3D Systems & Cloud Consultant
> LA ACM SIGGRAPH Chair
> President, Daly Realism - /Creating the Future/
> 
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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