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

On Sat, Mar 22, 2014 at 1:08 AM, Ladislav Lhotka <lhotka@nic.cz> wrote:

> Andy Bierman <andy@yumaworks.com> writes:
>
> > 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.
>
> An option for boolean-type properties is to wrap the affected object or
> value, e.g.
>
> "@protect": {
>     "host-name": ...
> }
>
> or
>
> "foo" : [ 1, 2, {"@protect": 3}, 4]
>
> Instead of defining a general JSON equivalent of XML attributes, it might
> actually be easier to come up with an ad hoc representation for every use
> case. This is the approach of some native JSON applications such as MongoDB.
>
> So, the specification of each global property (e.g. "protected") would
> also define an appropriate encoding in both XML and JSON.
>
> >
> > 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?
>
> "@owned-object": {
>     "@owner": "system",
>     "host-name": "router"
> }
>
>
Can you show how 2 list entries and 2 leaf-list entries
have different attribute values.  Of course we need to
support string values, not just boolean.

> Lada
>

Andy

>
> >
> >
> >
> > 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
> >>
> >>
> >>> _______________________________________________
> >>> netmod mailing list
> >>> netmod@ietf.org
> >>> https://www.ietf.org/mailman/listinfo/netmod
> >>>
> >>
> >>
> > _______________________________________________
> > netmod mailing list
> > netmod@ietf.org
> > https://www.ietf.org/mailman/listinfo/netmod
>
> --
> Ladislav Lhotka, CZ.NIC Labs
> PGP Key ID: E74E8C0C
>