[netmod] 答复: A question about YANG identifier design

yuchaode <yuchaode@huawei.com> Wed, 25 May 2022 01:36 UTC

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From: yuchaode <yuchaode@huawei.com>
To: 'Jürgen Schönwälder' <j.schoenwaelder@jacobs-university.de>
CC: "'netmod@ietf.org'" <netmod@ietf.org>, "'netconf@ietf.org'" <netconf@ietf.org>, Fatai Zhang <zhangfatai@huawei.com>, Zhenghaomian <zhenghaomian@huawei.com>, liuzhoulong <liuzhoulong@huawei.com>, "Chenchunhui (C)" <chenchunhui@huawei.com>
Thread-Topic: [netmod] A question about YANG identifier design
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Date: Wed, 25 May 2022 01:36:43 +0000
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Subject: [netmod] 答复: A question about YANG identifier design
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Thank you, Jürgen!

A generic identifier design is quite good for the other generic model design, just like the hardware components design mentioned by you.
But there have been some other models defined in a nesting level already, for example network topology and TE topology etc. If we want to reference a termination-point object, we need to specify its belonging network-id and node-id.
So for this kind of model, can we retrieve or reference terminal branch objects without its trunk branch objects' identifier if the RESTCONF server can guarantee the global uniqueness of terminal branch objects' identifier.
Just like the URL I mentioned in last email:

发件人: Jürgen Schönwälder [mailto:j.schoenwaelder@jacobs-university.de] 
发送时间: 2022年5月24日 18:16
收件人: yuchaode <yuchaode@huawei.com>
抄送: 'netmod@ietf.org' <netmod@ietf.org>; 'netconf@ietf.org' <netconf@ietf.org>; Fatai Zhang <zhangfatai@huawei.com>; Zhenghaomian <zhenghaomian@huawei.com>; liuzhoulong <liuzhoulong@huawei.com>; Chenchunhui (C) <chenchunhui@huawei.com>
主题: Re: [netmod] A question about YANG identifier design

You need to fit your data model to the data modeling language and the protocol. This can be a challenge at times but this is what it is.

>From what you are writing, it seems that you try to encode the
containment relationship of hardware components into the nesting levels of a YANG model.  This is likely not a good idea to start with and this may be the root cause of the problems you are facing. Note how RFC 8348 defines a hardware model that is essentially a flat list of hardware components and the containment relationship is modeled by additional contains-child etc. leafs. This approach gives us a simple /hardware/component/name that can be used to refer to any hardware component easily. Sure, the downside is that retrieving all components contained in another components is a bit more complex but being able to reference all hardware components in the same way likely is a big enough advantage to go for a flat list. (And once you think about it, the containment relationship is just one relationship, there may be others. By using a flat list with leafs, you can model multiple


On Tue, May 24, 2022 at 09:39:21AM +0000, yuchaode wrote:
> Hello friends,
> I have got some puzzles about YANG model design, to be more specific, it is about the identifier design in YANG model.
> As we know, YANG model is a tree-like structure, different objects are defined in different branches according their different levels. E.G. there is such a YANG tree:
> module: ietf-example
>    +--rw root
>       +--rw list-a* [leaf-1]
>          +--rw leaf-1    yang:uuid
>          +--rw leaf-2?   string
>          +--rw list-b* [leaf-3]
>             +--rw leaf-3    yang:uuid
>             +--rw leaf-4?   string
>             +--rw list-c* [leaf-5]
>                +--rw leaf-5    yang:uuid
>                +--rw leaf-6?   string
> List-c is child object of list-b and list-b is child object of list-a.
> If we want to retrieve a list-c instance, we need to know his parent list-b's and his grandparent list-a's identifier to construct a RESTCONF GET request URL:
> https://{{host:port}}/{{restconf}}/data/ietf-example:root/list-a={leaf-1}/list-b={leaf-3}/list-c={leaf-5}.
> However, you can easily find that the identifier of list-a, list-b and list-c are all UUID format. Usually, UUID is required to be unique globally. If the RESTCONF server complies with UUID requirement strictly, the identifier of list-b and list-a are redundant.
> Similarly, if there is a YANG data model want to reference list-c in its model, the reference identifier should include list-b and list-a's identifier at the same time besides list-c's identifier. If this list-c instance repeat a lot of time in this data model, there would be a lot of redundant list-b & list-a's identifier.
> Besides, this hierarchical identifier brings some problems when we are designing generic model. For example, if we want to design an alarm model, considering that the main information of alarm includes alarm ID, alarm level, tips message, location etc. which are generic for all inventory objects, it is easy for us to choose to design a generic model. For the inventory object alarm happened on, we would like to use a generic inventory resource type and resource UUID to specify. But if we use hierarchical identifier, considering alarm could be happened on NE, board or port .etc. and NE contains boards and board contains ports, we cannot use a generic identifier attribute to specify NE, board and port at the same time. For NE, we need to use one attribute to define its ne-id. And for board we need two attributes to define its id, ne-id and board-id. And for port, we need three attributes to define its id, ne-id, board-id and port-id.
> So I am wondering if for those objects which are using UUID as identifier, the server should implement this UUID globally unique. When retrieving these objects, there is no necessary to specify their parent's and grandparent's identifier. Just take the list-c retrieval above for example, the URL could be changed to be:
> https://{{host:port}}/{{restconf}}/data/ietf-example:root/list-a/list-b/list-c={leaf-5}<https://%7b%7bhost:port%7d%7d/%7b%7brestconf%7d%7d/data/ietf-example:root/list-a/list-b/list-c=%7bleaf-5%7d>. And for model object reference scenario, we can also use list-c's identifier only.
> This is just my consideration, any comments are welcome! Thank you!
> B.R.
> Chaode

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Jürgen Schönwälder              Jacobs University Bremen gGmbH
Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen | Germany
Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>