Hi,
While preparing draft-ietf-netmod-yang-data-ext-02, it turned out that
it is not clear what, if any, restrictions should be enforced for
yang-data structures. Even among the authors we have different ideas
for how this should work.
Background:
In 8040, the original yang-data extension had a restriction that said
that a yang-data structure MUST have exactly one container, since it
wouldn't be possible to have a yang-data structure in an XML instance
document otherwise.
Since people want to use yang-data structures in other places, this
restriction was lifted in the new draft:
There is no longer an assumption that a yang data structure can
only be used as a top-level abstraction, instead of nested within
some other data structure.
With this in mind, here's a use case that I think we ought to support:
rpc my-first-rpc {
description
"Bla bla...
If an error occurs, <error-info> will contain an instance of
the yang-data structure 'my-first-rpc-error-info'.";
...
}
yang-data my-first-rpc-error-info {
leaf reason { ... }
container user-info { ... }
}
rpc my-second-rpc {
description
"Bla bla...
If an error occurs, <error-info> will contain an instance of
the yang-data structure 'my-second-rpc-error-info'.";
...
}
yang-data my-second-rpc-error-info {
leaf reason { ... }
leaf important-url { ... }
}
(maybe in the future we could even have a YANG extension statement to
formalize the description:
rpc my-first-rpc {
...
opx:error-info-structure my-first-rpc-error-info;
}
but this is not point now.)
In the example above, note that the leaf "reason" is present in both
structures. IMO this is not a problem, since these structures are
used in different contexts.
My point is that I think we should impose as few restrictions as
possible to the yang-data extension. It should be up to the user of
yang-data to ensure that the structure is defined in such a way so
that it can be used properly. For example, a structure that is
supposed to describe an XML instance document cannot define two leafs
at the top level.
If the WG agrees with what I wrote above, we need to change the
augment-yang-data extension so that you would write for example:
yx:augment-yang-data /ex:my-first-rpc-error-info/ex:user-info {
...
}
Comments?
/martin
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