Re: [netconf] YANG attributes in a datastore

On Tue, 2019-12-10 at 14:58 +0000, Balázs Lengyel wrote:
> Hello,
> If we try to standardize editing metadata, we will face a number of issues
> that need to be clarified:
> 
> - Will you model whether the attribute (metadata) is writable?  Config is
> not an allowed substatement in https://tools.ietf.org/html/rfc7952#section-3

In my view annotations should never be configuration because they should not
influence the device state. The read-only/read-write propertly might be useful.

> - Can a metadata have other additional properties? (mandatory, cardinality,
> uniqueness of some kind?)

By design, annotations do not have a specific place in the schema, so they
cannot be mandatory.

Cardinality: if you mean annotations with a list of values, this was discussed
but rejected due to difficulties with XML encoding.

> - If it is modified, will it be subject to validation, error-messages? Will
> a bad metadata result in a failed error-config?

I would say yes because otherwise it makes no sense to define them and their
properties.

Lada

> 
> Regards Balazs
> 
> -----Original Message-----
> From: netconf <netconf-bounces@ietf.org> On Behalf Of Martin Bjorklund
> Sent: 2019. december 10., kedd 15:04
> To: mvasko@cesnet.cz
> Cc: netconf@ietf.org
> Subject: Re: [netconf] YANG attributes in a datastore
> 
> Hi,
> 
> Michal Vaško <mvasko@cesnet.cz> wrote:
> > Hello,
> > we are thinking about adding support for arbitrary attributes [1] in 
> > our YANG/NETCONF datastore. To my knowledge, only the representation 
> > in XML or JSON is defined and standardized but there are no guidelines 
> > for editing (CRUD) these attributes.
> > 
> > So, my question is a rather general one, regarding implementations 
> > that support editing these attributes, would you mind sharing some 
> > basic ideas or principles used? Or is this outside any consensus and 
> > each implementation is free to handle this completely in its own 
> > fashion? Thanks for any input.
> 
> I think this depends on the attribute defintion.  Some attributes are
> read-only from the northbound's protocol point of view.  Internally in the
> server you may need some API to set/change them of course.  Some other
> attributes are read-write.
> 
> In our implementation we support a few read-write attributes (and some
> read-only).  Here's a simple example (in an edit-config):
> 
>   <foo annotation="hello"/>
> 
> This would set/change the "annotation" attribute's value to "hello",
> regardless of its previous value.
> 
> To delete an annotation, you would do:
> 
>   <foo annotation=""/>
> 
> Each of our attributes has a special value that means "delete" (in most
> cases it is the empty string.
> 
> 
> /martin
> 
> 
> 
> 
> > Regards,
> > Michal
> > 
> > [1] https://tools.ietf.org/html/rfc7952
> > 
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> > 
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Ladislav Lhotka
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