Re: [netmod] WHEN statement within mandatory objects doesn't ensure presence of the mandatory object

["Sterne, Jason (Nokia - CA/Ottawa)" <[e-mail]>]

Hi Mike,
Please see below.
Jason

From: netmod <[e-mail]> On Behalf Of Michael Rehder
Sent: Tuesday, October 9, 2018 1:51 PM
To: [e-mail]
Subject: [netmod] WHEN statement within mandatory objects doesn't ensure presence of the mandatory object

I have a question about “when” and mandatory objects.

It seems to me that the implemented semantics of “when” are really “optional when”, in that the enclosing object can be absent even though it is mandatory and the “when” clause holds true.
The RFC could be clearer about this.

Example

   leaf color {
     enumeration  {
        enum “blue”;
        enum “black”;
     }
     mandatory true;
   }
   container foo {
      when ../color = ‘blue’;
      etc.
   }

“foo” is optional due to the presence of the “when” statement even though the object is mandatory (same is true for mandatory leaf, min-elements=1 list etc.).
[>>JTS: ]  What do you mean by "the object is mandatory" ?  I see that leaf color is mandatory (so it must have a value of either black or blue).  But the container foo is not mandatory.

This is considered valid XML for the above
    <color>blue</color>

In my view this makes conditionally variant schemas “loose” in their enforcement (some scenarios can use choice but it doesn’t cover everything).

I think that mandatory should be respected for the enclosing objects of a “when” statement.
That is, a mandatory object must be present when its “when” clause holds true and a Schematron statement should enforce that.
[>>JTS: ] We can't change that definition now. I don't know all the details of the rationale but "when" is defined such that its parent data definition statement is only valid when the condition in the "when" is true. But that doesn't mean that parent node is mandatory. In other words -> a "when" can only remove a node (from the schema), it can't enforce that a node exists (in instance data).

What is the rationale behind the current YANG rules behavior, that the “when” Schematron mapping doesn’t check for presence of the enclosing mandatory object?

thanks
Mike Rehder


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