On Tue, May 24, 2016 at 12:13:04PM +0200, Martin Bjorklund wrote:
> Juergen Schoenwaelder <j.schoenwael...@jacobs-university.de> wrote:
> > On Tue, May 24, 2016 at 10:33:29AM +0200, Martin Bjorklund wrote:
> > > 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.
> > >
> >
> > I will give it a try. I think it is helpful to define referring node
> > and referred node
>
> Ok.
>
> > and I think it is useful to first state the purpose
> > of the leafref type.
> >
> > The leafref type is restricted to the value set of some leaf node in
> > the schema tree and optionally further restricted by corresponding
> > instance nodes in the data tree. More precisely, the leafref type
> > declares a constraint on the value space of a leaf node (the
> > referring leaf node), based on a reference to a another leaf node in
> > the schema tree (the referred leaf node). The "path" substatement
> > (Section 9.9.2) is used to identify the referred leaf node in the
> > schema tree. The value set of the referring leaf node is the value
> > set of the referred leaf node if the "require-instance" property is
> > "false".
>
> Maybe remove the second sentence. Also s/value set/value space/.
> Also the last sentence isn't correct; the value space is always the
> value space of the referred node.
>
> > If the "require-instance" property is "true", there MUST exist an node
> > in the data tree, or a node with a default value in use (see Section
> > 7.6.1 and Section 7.7.2), of the referred schema tree leaf node with
> > the same value as the leafref value in a valid data tree.
> >
> > If the referring leaf node represents configuration data, and the
> > "require-instance" property (Section 9.9.3) is "true", the referred
> > leaf node MUST also represent configuration.
>
> Also, the text needs to mention leaf-lists. This gives:
>
>
> The leafref type is restricted to the value space of some leaf or
> leaf-list node in the schema tree and optionally further restricted
> by corresponding instance nodes in the data tree. The "path"
> substatement (Section 9.9.2) is used to identify the referred leaf
> or leaf-list node in the schema tree. The value space of the
> referring node is the value space of the referred node.
>
> If the "require-instance" property is "true", there MUST exist an
> node in the data tree, or a node with a default value in use (see
> Section 7.6.1 and Section 7.7.2), of the referred schema tree leaf
> or leaf-list node with the same value as the leafref value in a
> valid data tree.
>
> If the referring node represents configuration data, and the
> "require-instance" property (Section 9.9.3) is "true", the referred
> node MUST also represent configuration.
>
Works for me.
/js
--
Juergen Schoenwaelder Jacobs University Bremen gGmbH
Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
Fax: +49 421 200 3103 <http://www.jacobs-university.de/>
_______________________________________________
netmod mailing list
netmod@ietf.org
https://www.ietf.org/mailman/listinfo/netmod
