Re: [netmod] attributes in draft-lhotka-netmod-yang-json

On Thu, Mar 20, 2014 at 8:25 AM, Andy Bierman <andy@yumaworks.com> wrote:

>
>
>
> On Thu, Mar 20, 2014 at 7:04 AM, Martin Bjorklund <mbj@tail-f.com> wrote:
>
>> Dean Bogdanovic <deanb@juniper.net> wrote:
>> > Hi,
>> >
>> > In draft yang leaf node is defined as name value pair in json
>> >
>> > If it would be represented, as an object then we can assign attributes
>> to it.
>> >
>> > Example
>> > "host-name" {
>> >    "data" : "router",
>> >       "attributes" : { "protect" : protect}
>> > }
>> >
>> > We need attributes for several things, so lets try to figure out how to
>> enable
>> > them.
>>
>> I agree that the lack of attributes is a problem with the JSON
>> mapping.
>>
>> The problem with your solution is that it adds noise to the normal
>> case where there are no attributes.  We're using another encoding:
>>
>>    "host-name": "router",
>>    "@host-name": {
>>        "protect": "protect",
>>        ...
>>     }
>>
>> Yep, not very elegant...
>>
>>

More importantly, it doesn't work for lists or leaf-lists.
The attributes cannot be siblings (or ancestors) of the target data node.

Consider the following YANG data-stmt, and how an attribute
would be encoded in every data node (as a worse-case example).

container top {
  list A {
    key id;
    leaf id { type string; }
    leaf-list aa { type int8; }
  }
  leaf host-name { type string; }
}

Plain JSON

{ "top" : {
  "A" : [
    { "id":"entry-1",
      "aa": [42, 19]
    },
    { "id":"entry-2",
      "aa" : [99, 11]
    } ]
  },
  "host-name":"router"
}

Add attribute to each node:
   leaf owner { type string; }

With Owner Attribute using RESTCONF encoding:

{ "top" : {
  "@owner":"system",
  "A" : [
    { "@owner":"admin1",
      "id" : {
        "@owner":"admin1",
        "id": "entry-1"
      },
      "aa" : [ { "@owner":"admin1",  "aa": 42 },
                 { "@owner":"admin1",  "aa": 19 } ]
    },
    { "@owner":"admin2",
      "id" : {
        "@owner":"admin2",
        "id": "entry-2"
      },
      "aa" : [ { "@owner":"admin2",  "aa": 99 },
                 { "@owner":"admin2",  "aa": 11 } ]
    } ]
  },
  "host-name" : { "@owner":"system",
                         "host-name":"router" }
}

This is not elegant either, but it works for all YANG node types.
How would your encoding look for this example?

Andy

>
> This is how RESTCONF encodes these attributes in a leaf:
> (see sec. 3.4.1)
>
>    "host-name" : {
>        "@protect" : "protect",
>        "host-name" : "router"
>    }
>
> Lada says that this is a YANG to JSON mapping and YANG has no attributes,
> so the attribute encoding is in RESTCONF.  I think it would be better
> if there was 1 mapping, instead of a different mapping in each protocol
> that uses this JSON encoding of YANG data.
>
> I do not think YANG needs to model attributes!
> The protocol may need to use them to tag data with meta-data.
> We do not need to model some leafs as attributes and others
> as child nodes in YANG data models.  Use RelaxNG instead
> of YANG to do that.
>
>
>
>
>> /martin
>>
>>
> Andy
>
>
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>
>