Re: [netmod] Text in import to indicate whether a module is needed as import-only or as implemented

On Wed, 2020-01-08 at 04:49 -0800, Andy Bierman wrote:
> 
> On Wed, Jan 8, 2020 at 1:11 AM Ladislav Lhotka <lhotka@nic.cz> wrote:
> > On Tue, 2020-01-07 at 14:29 +0000, Balázs Lengyel wrote:
> > > If that is the consensus, I can remove the description statements, no big
> > > deal. (I actually like the statements, but they are not important for this
> > > draft)
> > 
> > Of course, it is not that important, but I don't see how this information
> > could
> > be harmful, if it is included with the import. In my view, it is not meant
> > as a
> > conformance requirement but just an info from the module author about the
> > meaning of the import statement.
> > 
> 
> It adds a lot of extra work but more importantly the import-stmt is the wrong
> place

What work do you mean? I thought that it would be just info for potential
developers (or their managers) that implementing the module requires
implementing other modules and functionality - or not. 

For example, if a module imports ietf-netconf-nacm only for using "node-
instance-identifier" type, it is relatively uninteresting. Otherwise,
implementation of the module may just be out of question.

> to document such a complex and unrelated issue as server conformance
> requirements.
> 
> 
> > The root of this problem (and design flaw of YANG, IMO) is that import is
> > "overloaded" with two different purposes, one of which effectively requires
> > that
> > the imported module be also implemented, while the other doesn't.
> > 
> 
> The import-stmt is only used to map a local prefix to an external module.

But one thing is using a prefix for accessing top-level types and groupings
(i.e. stuff in YANG modules), and another thing is accessing schema nodes, which
have to be present in the schema tree. In complicated data models, it is not
exactly easy to figure out all these dependencies.

So maybe what is really overloaded are the namespace prefixes: they are used for
addressing YANG modules, schema nodes and instances (in XPath). 

Lada

> This proposal to add conformance info the the import-stmt would overload it
> with
> another purpose.
> 
> Not even a typedef is easy to classify  (e.g., leafref requires implementation
> of a data node).
> I certainly agree that YANG conformance is poorly specified, poorly
> understood, and
> in real need of improvement. Likewise, the import-stmt is also in need of some
> improvement
> since import-by-exact-revision is (and has always been) poorly designed.
> 
> 
> > Lada
> > 
> > > Balazs
> 
> Andy
> 
>  
> > > -----Original Message-----
> > > From: Martin Bjorklund <mbj@tail-f.com> 
> > > Sent: Tuesday, January 7, 2020 2:38 PM
> > > To: Balázs Lengyel <balazs.lengyel@ericsson.com>
> > > Cc: andy@yumaworks.com; lhotka@nic.cz; netmod@ietf.org
> > > Subject: Re: [netmod] Text in import to indicate whether a module is
> > needed as
> > > import-only or as implemented
> > > 
> > > Hi
> > > 
> > > I agree w/ Andy and others that we should not add this to the import's
> > > description.  I don't think this kind of conformance text belongs to the
> > > import's description.  If you think it is important to state this, the
> > best
> > > place is probably as plain text in the document itself.
> > > 
> > > 
> > > 
> > > /martin
> > > 
> > > 
> > > Balázs Lengyel <balazs.lengyel=40ericsson.com@dmarc.ietf.org> wrote:
> > > > As a draft author who was asked to add text about the imports IMHO
> > > > 
> > > > *   it would be easy for me to remove the description from the import.
> > > > Actually I really just want to know what is acceptable to the group, so
> > I
> > > > can proceed
> > > > *   I also think that adding this text is in most cases easy and it does
> > not
> > > > need updates later.
> > > > *   The rules in some cases might not be trivial.
> > > > 
> > > > *   Imported YAMs need to be implemented if
> > > > 
> > > > *   Imported parts are included in Xpath (augment, when, must, require-
> > > > instance)
> > > > 
> > > > *   Imported YAMs do not need to be implemented if only the following
> > are
> > > > used
> > > > 
> > > > *   Types
> > > > *   Features
> > > > *   extensions
> > > > 
> > > > *   Ambiguous if
> > > > 
> > > > *   groupings are used
> > > > *   if the dependency is not formally defined by YANG, but functionally
> > > > needed. (E.g. notification-capabilities does not formally need YANG-
> > > > Push 
> > to
> > > > be implemented, however there is no sense in defining capabilities if
> > YANG-
> > > > Push is itself not implemented.)
> > > > *   deviation ?
> > > > *   other cases ?
> > > > 
> > > > Regards Balazs
> > > > 
> > > >  
> > > > 
> > > > From: netmod <netmod-bounces@ietf.org> On Behalf Of Andy Bierman
> > > > Sent: 2019. december 19., csütörtök 17:23
> > > > To: Ladislav Lhotka <lhotka@nic.cz>
> > > > Cc: NetMod WG <netmod@ietf.org>
> > > > Subject: Re: [netmod] Text in import to indicate whether a module is 
> > > > needed as import-only or as implemented
> > > > 
> > > >  
> > > > 
> > > >  
> > > > 
> > > >  
> > > > 
> > > > On Thu, Dec 19, 2019 at 8:00 AM Ladislav Lhotka <lhotka@nic.cz <mailto:
> > > > lhotka@nic.cz> > wrote:
> > > > 
> > > > On Thu, 2019-12-19 at 07:52 +0000, Schönwälder, Jürgen wrote:
> > > > > On Thu, Dec 19, 2019 at 08:23:27AM +0100, Ladislav Lhotka wrote:
> > > > > > I don't see how YANG syntax defines this. If a module imports 
> > > > > > ietf-netconf- acm, it could be because
> > > > > > 
> > > > > > - it just uses a typedef, such as "node-instance-identifier", and
> > then
> > > > > >   ietf-netconf-acm needn't be implemented (but can be),
> > > > > > 
> > > > > > or
> > > > > > 
> > > > > > - it augments ietf-netconf-acm, which makes sense only if the latter
> > > > > >   module is implemented.
> > > > > > 
> > > > > > It it the YANG library that specifies whether a module is 
> > > > > > implemented or not, but the "import" statement itself doesn't tell
> > you
> > > > > > anything.
> > > > > > 
> > > > > 
> > > > > Can we not assume that an implementor will figure out the difference?
> > > > 
> > > > An implementor should be able to figure it out, but other potential 
> > > > module users may not. For example, if somebody is evaluating whether 
> > > > to use a module for their device or not, it is important to know that 
> > > > NACM has to be implemented (or not).
> > > > 
> > > >  
> > > > 
> > > > You seem to be talking about a new conformance documentation procedure
> > > > 
> > > > that attempts to solve the problem "to use modules A, B, and C 
> > > > together
> > > > 
> > > > to achieve some functionality X, all these conditions need to be met"..
> > > > 
> > > > (Sounds more like a problem for YANG Packages to solve)
> > > > 
> > > >  
> > > > 
> > > > IMO this is a much harder problem than something that can be solved
> > > > 
> > > > with extra description-stmt text. The writer is likely to get it wrong 
> > > > or not
> > > > 
> > > > keep it up to date, so a tool to analyze the file seems like a better
> > > > solution.
> > > > 
> > > >  
> > > > 
> > > > Lada
> > > > 
> > > >  
> > > > 
> > > >  
> > > > 
> > > > Andy
> > > > 
> > > >  
> > > > 
> > > > 
> > > > > Or someone writes a pyang plugin to determine from the schema tree 
> > > > > the kind of imports there are (for a given set of features).
> > > > > 
> > > > > /js
> > > > > 
> > > > --
> > > > Ladislav Lhotka
> > > > Head, CZ.NIC Labs
> > > > PGP Key ID: 0xB8F92B08A9F76C67
> > > > 
> > > > _______________________________________________
> > > > netmod mailing list
> > > > netmod@ietf.org <mailto:netmod@ietf.org> 
> > > > https://www.ietf.org/mailman/listinfo/netmod
> > > > 
-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67