Re: [netmod] WG Last Call: draft-ietf-netmod-schema-mount-07

[Ladislav Lhotka <[e-mail]>]

Juergen Schoenwaelder <[e-mail]> writes:

> On Thu, Nov 09, 2017 at 05:38:40PM +0000, Robert Wilton wrote:
>> 
>> > > > > 3. Sec 2.1 Glossary of New Terms:  "Schema" isn't actually defined
>> > > > > anywhere (RFC 7950 doesn't define this).  Should it be defined here?
>> > > > > The NMDA datastores draft had a similar issue and we choose to define
>> > > > > "datastore schema" instead.
>> > > > I think the right place for defining the term "schema" (and "data model"
>> > > > as well) is the specification of YANG because it is desirable that all
>> > > > documents related to YANG use the same meaning.
>> > > OK, 7950 doesn't define it today.  Is that a problem?
>> > "Schema tree" and "schema node" are defined and used a lot in 7950, so
>> > it might be good to define "schema" as well - meaning the schema tree
>> > with all associated semantics.
>> OK, but we can't add definitions to 7950 now.  Would it make sense to add
>> the definition to the NMDA draft and reference that?
>
> So what is the difference between "schema tree" and "schema"? Or to
> put it differently, what is "all associated semantics" that you are
> adding to a "schema tree" to obtain a "schema"? RFC 7950 says:
>
>    o  schema tree: The definition hierarchy specified within a module.

As Rob points out, this is probably incorrect, as schema tree should
involve multiple modules. It makes no sense to talk about a schema tree
of an augmenting module unless we also take into account the augmented
module.

Anyway, schema tree is really just the hierarchy, i.e. a tree of schema
nodes, whereas schema is the hierarchy with datatypes, semantic rules
and all that. We can validate instance data against the schema, not
against the schema tree. This is at least how I understand it.

Lada

>
> If I understand 'definition hierarchy' correctly, than it seems
> "schema" is just an abbreviation of "schema tree", i.e., there is no
> semantic difference between these two terms. If there is a difference,
> we need to be able to spell it out.
>
> /js
>
> -- 
> Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> Fax:   [phone]         <http://www.jacobs-university.de/>
>
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
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