Re: Blog: YANG Really Takes Off in the Industry

[Benoit Claise <[e-mail]>]

Hi Tom,
> ----- Original Message -----
> From: "Ted Lemon" <[e-mail]>
> To: "Dean Bogdanovic" <[e-mail]>
> Cc: "IETF-Discussion list" <[e-mail]>
> Sent: Tuesday, December 02, 2014 2:59 AM
> Subject: Re: Blog: YANG Really Takes Off in the Industry
>
>
> On Dec 1, 2014, at 8:54 PM, Dean Bogdanovic <[e-mail]> wrote:
>> this is one part I don't understand. Why adding another language would
> make them less agile?
>
> If the yang model isn't a good representation of what is being modeled,
> it can cause more harm than good.   Same problem exists with MIBs.
>
> <tp>
>
> The difference is that MIBs are written in a much simpler language; what
> object should there be, its syntax and status (index, read-only,
> read-write) and that's about it (even augmentation tends to confuse many
> people).  I have never yet met a MIB module that I could not reverse
> engineer to determine the design, even the requirements.
>
> YANG is different, it is capable of much more complicated things and
> occasionally it is unclear what it does mean (something that surfaces on
> the netmod WG list now and again).  What I think I see happening is what
> happened when programming languages became more widely used, an
> inability to keep things as simple as they could be, resulting in code
> whose purpose was unclear, that was error-prone and hard to understand
> or maintain.  Not an issue with SMI.
>
> The YANG models of the IETF seem to be diving into complex code from
> which it is hard to discern what the purpose is, and the fact that most
> of the exemplars are written by those highly expert in YANG, and so use
> the wide range of constructs available, does not help.
>
> Perhaps the IESG should require that any IETF YANG data model must be
> accompanied by an information model so that we can debate what should be
> done independently of deciding how to do it.  After all, this is a
> stricture that has been imposed on the I2RS WG.
Having information models (IM) before data models (DM) is the right 
theoretical approach. And I pushed that approach in the past, when YANG 
was not the data modeling of choice for configuration. I mean before the 
Writable MIB Module IESG Statement 
<https://www.ietf.org/iesg/statement/writable-mib-module.html>

However, I don't think it's appropriate any longer.
- what is the language for IM: text, UML, pseudo-code?
- when I discussed IM for DM with some operators, the answers were along 
these lines: "no IMs please, give me something that I can work with, so 
vendor-neutral DMs. And btw, this is urgent."
- as Alia mentioned, IM before DM didn't work too well for I2RS

In conclusion, at the time were DMs are urgent, I agree with Alia:

    "I'd rather see a section in the YANG model that describes the
    information and relationships - and then the pyang tree and the
    detailed model."

Regards, Benoit
>
> Tom Petch
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> When different implementations of the same thing use different base
> assumptions, it can be difficult to come up with a management model that
> is congruent with all of the different base assumptions and is still
> useful.   I wouldn't say it's impossible, but it's a good bet that a
> poorly thought out model or a model that is based on experience with a
> single implementation will fail in this regard.
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