[Bug 26938] [XDM31] Constraints on elements

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26938

Jonathan Robie <jonathan.robie@gmail.com> changed:

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--- Comment #1 from Jonathan Robie <jonathan.robie@gmail.com> ---
(In reply to Tim Mills from comment #0)
> Unless I'm missing something, the data model doesn't seem to constrain an
> element not to be a parent of itself explicitly.
> 
> There are some hints that this is the case, such as "Nodes form a tree." in
> section 2.1 Terminology.  It can be inferred from "2.4 Document Order" where
> a total order cannot be defined if a node can be its own parent.

I do believe that these statements give you what you need.

> I'd have hoped for a specific constraint in "3 Data Model Construction" but
> find:
> 
> "There are no constraints on how an instance of the data model may be
> constructed directly, save that the resulting instance must satisfy all of
> the constraints described in this document."
> 
> which seems a little recursive!

XQuery and XPath each have their own sections on consistency constraints, which
add further requirements. I don't think we should move these to XDM, that would
be a drastic restructuring of our work at this late stage.

> Another possible location for making this explicit would be in under
> "Element Nodes" in "6.2 Element Nodes" which currently reads:
> 
> * If a node N is among the children of an element E, then the parent of N
> must be E.
> * ... if a node N has a parent element E, then N must be among the children
> of E.
> 
> but this doesn't prevent a node being its own parent.
> 
> This has a bearing on the result of the XQuery Update expression
> 
> copy $node := <node />
> modify insert node $node into $node
> return $node

That's well specified in the XQuery Update Facility, using the current XDM.

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Received on Tuesday, 30 September 2014 12:08:56 UTC