Hi Vladimir,

We have one YANG file that represents multiple components in the system.  
Currently they are bundled together, so having a single YANG file is ok.  In 
future we’d like to be able to break this down into multiple daemons each 
dealing with a subset of the YANG.  However, we don’t wish to change the 
namespace of the YANG as that would not be backwards compatible.  So, 
submodules looked to be a good way to do this.  I wouldn’t call it drastic – it 
is one YANG file we are talking about breaking up into parts.



From: Vladimir Vassilev [mailto:vladi...@transpacket.com]
Sent: 07 August 2017 20:31
To: Ivory, William <william.iv...@intl.att.com>
Cc: 'netmod@ietf.org' <netmod@ietf.org>
Subject: Re: [netmod] Query about augmenting module from submodule in YANG 1.0

IMO "submodule"s  are a striking example of redundant complexity in an 
otherwise very close to perfection YANG (regardless if it is YANG 1.0 or 1.1).

Modules and submodules have been around for a while however the ratio of the 
currently published modules compared with the submodules is about 40 modules to 
1 submodule (if one ignores all the modules and submodules from  particular 
networking hardware manufacturer that is particularly keen on using 
submodules). As a far but still relevant analogy Java has a limitation of 1 
file per class and this atomicity has proven to be an advantage especially in 
terms of enforcing modularity. IMO there is nothing that can be done with the 
help of submodules that can not be done without them.

For the sake of the argument can you provide a synthesized description of the 
problem that lead you to a drastic solution like "we’ll look at trying to put 
everything into submodules in this case."?

On 08/07/2017 04:37 PM, Ivory, William wrote:
Hi Jan,

Thanks – we’ll look at trying to put everything into submodules in this case.



From: Jan Lindblad [mailto:j...@tail-f.com]
Sent: 07 August 2017 14:28
To: Ivory, William <wi2...@intl.att.com><mailto:wi2...@intl.att.com>
Cc: netmod@ietf.org<mailto:netmod@ietf.org>
Subject: Re: [netmod] Query about augmenting module from submodule in YANG 1.0

The submodule concept in YANG 1.0 is, well, not very useful, and even less 
intuitive. That's why it saw major rework in YANG 1.1.

A YANG 1.0 submodule cannot reference the module that includes it, directly or 
indirectly. This is because in YANG 1.0 the symbols in other submodules of the 
same namespace are invisible to the submodule unless they are explicitly 
included. And parent modules can't be included by a submodule because that 
would lead to an inclusion loop. It is possible to reference (augment, etc) 
other sibling submodules, though. So if you split your modules cleverly, you 
might be able to resolve your referential constraints anyway.

If you really want to take the submodule path, I'd recommend moving to YANG 
1.1. In the interest of preserving the hair tone of IT-architects.


We’re trying to solve a modularity problem with a YANG module by splitting it 
into submodules and augmenting the parent module from each submodule.  However, 
despite the wording below in YANG 1.0 section 7.15, we’ve found a couple of 
threads online with comments suggesting it’s only allowed in YANG 1.1?  Would 
appreciate clarification.

RFC 6020 section 7.15 suggests it is allowed:

   The "augment" statement allows a module or submodule to add to the
   schema tree defined in an external module, or the current module and
   its submodules, and to add to the nodes from a grouping in a "uses"

Versus online comments here: 

‘> On 01 Mar 2016, at 10:38, Anton Tkáčik <anton.tkacik at pantheon.tech> wrote:


> Hi,

> Noticed other issue with example set,

> In 
> https://github.com/mbj4668/pyang/issues/194<https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_mbj4668_pyang_issues_194&d=DwMFaQ&c=LFYZ-o9_HUMeMTSQicvjIg&r=FmJP9CH54z5mG3DFGBdc_9q1TLpYQ31-TQ-26_Qa9vw&m=YC4w6Zi9KhBp0MnnvA42_qdR2aM3uOFWpZYtgF122Ec&s=bkakKJEZzCBq3BkP5NzW-wDX6KOZHpOnT0u-ySg8rS0&e=>
>  Lada stated that in YANG 1.0 submodule can not augment nodes

> defined in parent model.


> Is that correct that submodule can not augment definition defined in parent 
> module?

This isn't possible in YANG 1.0 but will be possible in 1.1. However, in the 
present case the definition being augmented from the submodule is arguably in a 
different module.




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