Re: [netconf] YANG attributes in a datastore

On Tue, 2019-12-10 at 07:42 -0800, Andy Bierman wrote:
> Hi,
> 
> YANG already has the "annotation" statement to define metadata.
> YANG has data-def-stmt to define data.  It would be very unwise
> to use metadata inside a leaf as if it were a leaf inside a container.

A typical example is a "comment" annotation - you want to permit it basically
everywhere but don't want to clutter the schema with "comment" leaves.

Lada 

> 
> 
> Andy
> 
> 
> On Tue, Dec 10, 2019 at 7:31 AM Ladislav Lhotka <lhotka@nic.cz> wrote:
> > 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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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
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