Re: [netmod] Materials for NETMOD Virtual Interim meeting (Monday)

If module A imports from module B, then the question whether a change
in module B is compatible or not for module A is answered by what
module A actually uses of module B's definitions. The question is not
answered by module B's version number.

The maintainer of module B can't tell whether her change breaks module
A without knowing A. And the maintainer of A can't predict how module
B will change in the future. As a consequence, the maintainer of A
cannot realiably decide whether revision-or-derived or
revision-or-derived-compatible is the right choice. The author of A
has to _guess_, having more options to guess may help, or it may
not. My point is that it is always a guess.

The maintainer of module B may be acting in a conservative way and
bumping major numbers frequently (and many times not affecting module
A) or maintainer B may be lenient - and B's decision may be influenced
by how central module B is, the more modules depend on B, the higher
the pressure to not bump the major version number of B and to either
avoid non-backwards compatible changes or to label them as compatible
(even though it is possible they are not).

In some realities, you end up with a need for more complex expressions
over the version number space to define which versions are known to
work together. And this information is often maintained _outside_ the
code artifacts (one advantage being that this makes dependency updates
possible without having to touch the files with the definitions). Some
examples:

https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html

https://cabal.readthedocs.io/en/latest/developing-packages.html#modules-imported-from-other-packages

https://semver.npmjs.com/

Given these examples, one can ask whether decorating the YANG import
statement with 'inline' versioning constraints is actually the right
way to go. Perhaps dependency constraints are better managed outside.

/js

On Fri, Dec 11, 2020 at 07:17:22PM +0000, Sterne, Jason (Nokia - CA/Ottawa) wrote:
> Hi all,
> 
> Enclosed are the materials for the Virtual Interim on Monday.  Have a good weekend!
> 
> Rgds,
> Jason

> _______________________________________________
> netmod mailing list
> netmod@ietf.org
> https://www.ietf.org/mailman/listinfo/netmod

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Juergen Schoenwaelder           Jacobs University Bremen gGmbH
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