> On 23 May 2016, at 16:10, Martin Bjorklund <[email protected]> wrote:
>
> Hi,
>
> This comment from the Gen-ART review deserves it's own thread.
>
> gen-art> - section 9.9
> gen-art>
> gen-art> The leafref type is used to declare a constraint on the value
> space
> gen-art> of a leaf, based on a reference to a set of leaf instances in the
> gen-art> data tree. The "path" substatement (Section 9.9.2) selects a set
> of
> gen-art> leaf instances, and the leafref value space is the set of values
> of
> gen-art> these leaf instances.
> gen-art>
> gen-art> The first sentence isn't quite right. Perhaps:
> gen-art>
> gen-art> The value space of a leaf with leafref type is one of the values
> of
> gen-art> a set of leaf instances in the data tree. The "path" substatement
> gen-art> (Section 9.9.2) selects the set of leaf instances, and the leafref
> gen-art> value space is the set of values of these leaf instances.
> gen-art>
> gen-art> - section 9.9.3
> gen-art>
> gen-art> If "require-instance" is "true", it means that the instance being
> gen-art> referred MUST exist for the data to be valid. This constraint is
> gen-art> enforced according to the rules in Section 8.
> gen-art>
> gen-art> If "require-instance" is "false", it means that the instance being
> gen-art> referred MAY exist in valid data.
> gen-art>
> [...]
> gen-art> Also, I think the second paragraph means that if require-instance is
> gen-art> false, the referred-to instance need not exist. But it's not clear
> to
> gen-art> me what that would mean -- if there are no instances referenced by
> the
> gen-art> XPath expression, then the set of value values of the leafref would
> be
> gen-art> empty and the leafref would necessarily be invalid. ... I think
> these
> gen-art> paragraphs need to be expanded in some way.
>
> mbj> Right; so what we want to say is:
> mbj>
> mbj> - the value space is the same as the value space of the referred
> mbj> leaf
> mbj>
> mbj> - there is an additional constraint if require-instance is true that
> mbj> the referred to leaf instance must exist
> mbj>
> mbj> How about
> mbj>
> mbj> OLD:
> mbj>
> mbj> The leafref type is used to declare a constraint on the value space
> mbj> of a leaf, based on a reference to a set of leaf instances in the
> mbj> data tree. The "path" substatement (Section 9.9.2) selects a set of
> mbj> leaf instances, and the leafref value space is the set of values of
> mbj> these leaf instances.
> mbj>
> mbj> If the leaf with the leafref type represents configuration data, and
> mbj> the "require-instance" property (Section 9.9.3) is "true", the leaf
> mbj> it refers to MUST also represent configuration. Such a leaf puts a
> mbj> constraint on valid data. All such nodes MUST reference existing
> mbj> leaf instances or leafs with default values in use (see Section 7.6.1
> mbj> and Section 7.7.2) for the data to be valid. This constraint is
> mbj> enforced according to the rules in Section 8.
> mbj>
> mbj> NEW:
> mbj>
> mbj> The leafref type is used to declare a constraint on the value space
> mbj> of a leaf, based on a reference to a set of leaf instances in the
> mbj> data tree. The "path" substatement (Section 9.9.2) is used to refer
> mbj> to another leaf node. The leafref value space is the value space of
> mbj> this leaf node.
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"?
Lada
> mbj>
> mbj> If the "require-instance" property is "true", there MUST exist an
> mbj> instance, or a leaf with a default value in use (see Section 7.6.1
> mbj> and Section 7.7.2), of the leaf being referred to with the same value
> mbj> as the leafref value in a valid data tree.
> mbj>
> mbj> If the leaf with the leafref type represents configuration data, and
> mbj> the "require-instance" property (Section 9.9.3) is "true", the leaf
> mbj> it refers to MUST also represent configuration.
>
>
> Does anyone have comments on this proposal?
>
>
> /martin
>
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Ladislav Lhotka, CZ.NIC Labs
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