Hello,
Yes this is similar to your proposal, so we should be able to hammer out
something.
I am happy to see you agree that this is an important use-case, YANG
needs to support.
Solution: My problem is that the specific data in the yang-library or in
ietf-yang-schema-mount is only defined and available in run-time, so I
don't understand how it could solve the design-time schema-mount
requirement. IMHO whatever the solution, it needs to be in a file.
Procedure: I assume we will not update the YANG language in the next
year or more, so I don't see what else can we do beside yang-extensions.
In one other modeling environment it is common practice, that new
modeling concepts are first introduced as extensions, then at every
release of the model language the important extensions are incorporated
as proper language statements. This gives a fast path to implement new
things, provides a method to "experiment" with new things and to do a
shake-down on new things before they are incorporated into the modeling
language. Again I don't insist on extensions, but what is the alternative?
Balazs
On 2016-07-28 15:05, Ladislav Lhotka wrote:
Hi Balazs,
I agree with you, we need a machine-readable offline specification of
the entire schema. After Martin returns from his vacation, I plan to
discuss this with him.
Some comments are inline.
Balazs Lengyel <[email protected]> writes:
Hello,
As I understand it, Schema-mount today does not support an important
use-case which we definitely need, but others also indicated they
want.
I want to specify off-line in design time which models will be mounted
where. Many of my nodes know in design-time what their model structure
will be, so I want a way to be able to document this in YANG. In
today's proposal the only way to find the Yang-Mounts is to read it
from the live node.
* OAM integrators or operators want to be able to write CLI scripts
and Netconf messages without accessing (expensive) real nodes. For
this they need to know the mounts
* We want to generate some fancy documentation from YANG automatically
in design-time.
In fact, I met several people in Berlin that expect to be able to
standardise data models utilising schema-mount.
* Many use cases need the possibility to mount schemas, but do not
need the added complexity of schema changes in run-time.
Notwithstanding the case of "YANG Features", for me the model schema
is a mostly static description of a nodes capabilities. Most of the
time I do not want to worry about the node changing its schema on
the fly.
For this I propose 2 YANG extensions
extension schema-mount {
description "Indicates that a YANG Module is to be mounted into
another module.
The argument specifies the name of the module to be mounted.";
argument mounted-module;
}
extension schema-mount-target {
description "Specifies the target node under which a YANG module is to
be mounted.
The statement can only be used inside a schema-mount statement.
The argument follows the same rules as an augment statement's target.
argument target-node;
}
This looks similar to the RELAX NG "external" pattern that I briefly
described in slide 9 of my presentation in Berlin:
https://www.ietf.org/proceedings/96/slides/slides-96-netmod-7.pdf
However, I am not in favour of introducing extesions for such
fundamental data modelling functions because doing so undermines the
value of YANG as a standard.
That's why I would prefer to use a solution based on a meta-schema
language (see my slide 10). After all, YANG library in fact already is a
meta-schema language, so we could just extend it to support schema
mount.
Lada
The two extension statements can be placed in a separate module or the
mounted module.
I don't insist on the solution, but I need the off-line/design-time
specification of yang-mount to be possible. IMHO the design-time mount
use-case is more important than the dynamic-mount.
regards Balazs
--
Balazs Lengyel Ericsson Hungary Ltd.
Senior Specialist
Mobile: +36-70-330-7909 email: [email protected]
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Balazs Lengyel Ericsson Hungary Ltd.
Senior Specialist
Mobile: +36-70-330-7909 email: [email protected]
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