Re: [netmod] Y34

[Ladislav Lhotka <[e-mail]>]

> On 20 Jul 2015, at 23:00, Juergen Schoenwaelder <[e-mail]> wrote:
> 
> Lada,
> 
> Y34 is closed and I have not seen any new argument here that indicates
> we made a major mistake with the resolution of Y34. As such, Y34
> remains closed.

Of course, I was expecting this reaction. I think I did present *some* arguments, and I am leaving it to others to judge whether they are relevant or not. Even if it was a minor mistake, it is IMO still worth fixing.

> 
> If you want to discuss new ideas to relocate or "symlink" data models,
> please do so in a separate thread. (And no, we do not accept new
> issues for YANG 1.1 either at this point in time.)

It’s not about symlinks in the data tree but rather about a method for combining schemas that is complementary to “augment” - pull versus push.

There is sufficient evidence that it was one of the use cases for “anydata”, e.g. in configlets. The gap in “anydata” definition for similar use cases is that it cannot specify a schema for its contents.

Lada 

> 
> /js
> 
> On Mon, Jul 20, 2015 at 07:42:49PM +0200, Ladislav Lhotka wrote:
>> 
>>> On 20 Jul 2015, at 19:29, Andy Bierman <[e-mail]> wrote:
>>> 
>>> 
>>> 
>>> On Mon, Jul 20, 2015 at 10:15 AM, Ladislav Lhotka <[e-mail]> wrote:
>>> 
>>>> On 20 Jul 2015, at 17:00, Andy Bierman <[e-mail]> wrote:
>>>> 
>>>> 
>>>> 
>>>> On Mon, Jul 20, 2015 at 6:08 AM, Ladislav Lhotka <[e-mail]> wrote:
>>>> 
>>>>> On 20 Jul 2015, at 14:55, Andy Bierman <[e-mail]> wrote:
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> Can you explain why we need 2 broken anyxmls?
>>>>> (The original and a synonym?)  The whole point of
>>>>> anydata is that it does not have XML cruft in it.
>>>> 
>>>> Yes, I understand this was your main priority. For implementors using off-the-shelf XML parsers and tools the XML cruft is not an issue at all.
>>>> 
>>>> 
>>>> yes it is an issue.
>>>> We need something to model a container full of arbitrary YANG data nodes.
>>>> This is something that can be applied to the contents of a datastore.
>>> 
>>> anyxml can do that, too.
>>> 
>>> 
>>> the WG already decided it can't.
>>> The extra XML PIs, etc. are not accepted by all servers, remember?
>>> There is no use for the extra stuff in the datastore.
>>> I don't see why we need 2 anyxml constructs that are not
>>> supported by the industry.  One is already too many.
>> 
>> I agree, but this is what we are going to have. My proposal was to have just one with two different names.
>> 
>>> 
>>> 
>>>> 
>>>> 
>>>> Anyway, I believe there are use cases for arbitrary XML/JSON/CBOR/… with no (YANG) schema available. My only complaint to “anyxml” has always been that it is a misnomer for encodings other than XML.
>>>> 
>>>> The message encoding on the wire is not the same issue
>>>> as the contents of a datastore.  Our server stores its own
>>>> internal data structures.  XML, JSON, CBOR are just message
>>>> encoding formats between client and server.  The datastore
>>>> is not encoded in any of these formats.
>>> 
>>> The payload of anyxml needn’t directly map to a data subtree in the usual sense.
>>> 
>>> that's precisely the difference between anyxml and anydata.
>>> The anydata node MUST map directly into data subtrees.
>> 
>> If the server doesn’t know the YANG data model at run time (which is possible) then it cannot do it - for instance, it cannot properly map module names to namespace URI or handle lists.
>> 
>>> 
>>> 
>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>>> 
>>>>> I also don't get the value of a single top-level node called 'device'
>>>>> that every YANG model on the planet is supposed to augment.
>>>>> Can you explain why a protocol operation to retrieve the
>>>>> document root (/) is not sufficient for the top-level node?
>>>> 
>>>> I don’t intend to defend their model, the more serious problem IMO is that a model for a single device/function may be needed in another device that hosts many virtualised devices/functions of the former type. We don’t have a good solution for this rather typical situation.
>>>> 
>>>> But a single container called "whatever" provides no such aggregation.
>>>> You would need a list for that. And the NMS might have multiple
>>>> layers of hierarchy to represent various aggregations.  The NP
>>>> container called "device" is not helpful for aggregation.
>>> 
>>> The parent node can be a list as well. The “root” node would be like a mount point in a Unix filesystem.
>>> 
>>> 
>>> Are you saying all data on a device needs to be in a top-level list called 'device'
>>> because an NMS might exist that  wants to have the datastores from lots of devices?
>>> As Martin pointed out several times, the NMS can make its own container or
>>> lists.  It does not need the device to mirror its own structure.
>> 
>> As I said, I don’t care that much about the “device” container. What would be really useful is to have the possibility to do e.g. this:
>> 
>> virtual-node* [name]
>>    name
>>    if:interfaces
>>        ...
>> 
>> to support the use case where all virtual nodes are managed by the same NETCONF/RESTCONF server.
>> 
>> Lada
>> 
>>> 
>>> 
>>> 
>>> Lada
>>> 
>>> Andy
>>> 
>>> 
>>>> 
>>>> 
>>>> 
>>>> Lada
>>>> 
>>>> 
>>>> Andy
>>>> 
>>>> 
>>>>> 
>>>>> Andy
>>>>> 
>>>>> 
>>>>> 
>>>>> On Mon, Jul 20, 2015 at 5:48 AM, Ladislav Lhotka <[e-mail]> wrote:
>>>>> 
>>>>>> On 20 Jul 2015, at 14:45, Ladislav Lhotka <[e-mail]> wrote:
>>>>>> 
>>>>>> Hi,
>>>>>> 
>>>>>> after listening to the presentation of
>>>>>> draft-rtgyangdt-rtgwg-device-model-00 at RTGWG session, I am wondering
>>>>>> whether the solution chosen for Y34 is really useful.
>>>>>> 
>>>>>> The draft states they want to reuse ietf-interfaces but their tree in
>>>>>> fact is
>>>>>> 
>>>>>>  +--rw device
>>>>>>         +--rw info
>>>>>>         |  +--rw device-type?   enumeration
>>>>>>         +--rw hardware
>>>>>>         +--rw interfaces
>>>>>>         |  +--rw interface* [name]
>>>>>>         |     ...
>>>>>>         +--rw qos
>>>>>> 
>>>>>> So the "interfaces" container is no more a top-level node. There are
>>>>>> three possible options:
>>>>>> 
>>>>>> 1. Change the ietf-interfaces module.
>>>>>> 2. Replicate its contents in another module.
>>>>>> 3. Extend YANG so that a *specific* schema tree can be grafted at a
>>>>>>  given data node.
>>>>>> 
>>>>>> IMO #1 & #2 are really bad. I thought Y34-04 was essentially #3 but it
>>>>>> seems it is not so because it doesn't specify a concrete data model
>>>>>> that's allowed at a given location.
>>>>>> 
>>>>>> On the other hand, the only real contribution of "anydata" over "anyxml"
>>>>>> is that is doesn't permit mixed content in XML, which is IMO not much.
>>>>>> 
>>>>>> I know Y34 was already closed but I think it is more important to do
>>>>>> things right before YANG 1.1 becomes an RFC.
>>>>>> 
>>>>>> What I want to propose is this:
>>>>>> 
>>>>>> - Rename "anydata" as a synonym to "anyxml", and deprecate "anyxml" (but
>>>>>> keep it for backward compatibility).
>>>>> 
>>>>> s/Rename/Introduce/
>>>>> 
>>>>>> 
>>>>>> - Introduce a new statement and data node type, e.g. "root", that will
>>>>>> extend the schema tree starting from that data node with a precisely
>>>>>> specified data model. The specification can be same or similar as
>>>>>> in yang-library.
>>>>>> 
>>>>>> I believe there are other use cases in the existing modules. For
>>>>>> example, the ietf-routing module could simply define the data model for
>>>>>> a single routing instance (i.e. without "routing-instance" list at the
>>>>>> top), and it can be then used without changes on simple devices, and
>>>>>> more complex router implementations can graft it as a subtree under
>>>>>> "routing-instance", "networking-instance" or whatever.
>>>>>> 
>>>>>> Lada
>>>>>> 
>>>>>> --
>>>>>> Ladislav Lhotka, CZ.NIC Labs
>>>>>> PGP Key ID: E74E8C0C
>>>>>> 
>>>>>> _______________________________________________
>>>>>> netmod mailing list
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>>>>>> https://www.ietf.org/mailman/listinfo/netmod
>>>>> 
>>>>> --
>>>>> Ladislav Lhotka, CZ.NIC Labs
>>>>> PGP Key ID: E74E8C0C
>>>>> 
>>>>> 
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> netmod mailing list
>>>>> [e-mail]
>>>>> https://www.ietf.org/mailman/listinfo/netmod
>>>>> 
>>>> 
>>>> --
>>>> Ladislav Lhotka, CZ.NIC Labs
>>>> PGP Key ID: E74E8C0C
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>>> --
>>> Ladislav Lhotka, CZ.NIC Labs
>>> PGP Key ID: E74E8C0C
>>> 
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> netmod mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/netmod
>> 
>> --
>> Ladislav Lhotka, CZ.NIC Labs
>> PGP Key ID: E74E8C0C
>> 
>> 
>> 
>> 
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> 
> -- 
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   [phone]         <http://www.jacobs-university.de/>

--
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C