Juergen Schoenwaelder <j.schoenwael...@jacobs-university.de> wrote:
> On Mon, May 23, 2016 at 05:29:42PM +0200, Ladislav Lhotka wrote:
>
> [...]
>
> > This mixes up paths in the data tree with those in the schema tree. The
> > XPath expression in the "path" statement is evaluated in the context of a
> > data tree, but if the result is an empty node set, then "this leaf node"
> > makes no sense.
> >
> > A specific example:
> >
> > leaf fooref {
> > type leafref {
> > path "../foo";
> > require-instance false;
> > }
> > }
> >
> > leaf foo {
> > type uint8;
> > when "../bar < 42";
> > }
> >
> > leaf bar {
> > type uint8;
> > default 100;
> > }
> >
> > If there is neither "foo" nor "bar" in the data tree, what is the value
> > space of "fooref"?
> >
>
> Hm. Is it not both? The path refers to a schema node in order to
> determine the base type (which is the base value set if
> require-instance is false). If require-instance is true, then there is
> an additional constraint that refers to a set of data nodes that
> essentially determine a (possibly empty) subset of the value space.
>
> If you agree with this, then we essentially have to phrase this
> clearly.
Exactly. My proposal was:
OLD:
The leafref type is used to declare a constraint on the value space
of a leaf, based on a reference to a set of leaf instances in the
data tree. The "path" substatement (Section 9.9.2) selects a set of
leaf instances, and the leafref value space is the set of values of
these leaf instances.
If the leaf with the leafref type represents configuration data, and
the "require-instance" property (Section 9.9.3) is "true", the leaf
it refers to MUST also represent configuration. Such a leaf puts a
constraint on valid data. All such nodes MUST reference existing
leaf instances or leafs with default values in use (see Section 7.6.1
and Section 7.7.2) for the data to be valid. This constraint is
enforced according to the rules in Section 8.
NEW:
The leafref type is used to declare a constraint on the value space
of a leaf, based on a reference to a set of leaf instances in the
data tree. The "path" substatement (Section 9.9.2) is used to refer
to another leaf node. The leafref value space is the value space of
this leaf node.
If the "require-instance" property is "true", there MUST exist an
instance, or a leaf with a default value in use (see Section 7.6.1
and Section 7.7.2), of the leaf being referred to with the same value
as the leafref value in a valid data tree.
If the leaf with the leafref type represents configuration data, and
the "require-instance" property (Section 9.9.3) is "true", the leaf
it refers to MUST also represent configuration.
Please comment and/or suggest improvements to this proposal.
/martin
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