Re: [yang-doctors] Unsupported schema tree w/ cyclic dependencies + schema node identifier clarification

Hi,

Ebben Aries <exa@arrcus.com> wrote:
> I have a few questions for the group that have surely come up before...
> but maybe I'm missing something...
> 
> 1. How to handle cases where you only support a non-schema tree portion
> of a module where other non-schema statements have a cyclic dependency
> back to the schema tree

Is this a separate question from 2 below?  If so, I don't understand
the question.  If it the same, please see below.

> 2. Schema Node Identifier wording in RFC7950
> 
> 
> For #1, Let's say you have module A that imports module B for use of an
> identity.  Let's call the use of this an identityref to 'base b:foo'
> 
> Module B contains typedefs, identities and schema tree and the
> implementation prefers to deviate the schema tree completely as
> 'not-supported' but needs to support this model for resolving imports
> and use of identities only (e.g. module A).

The server would advertise module B as conformance-type = import in
the YANG library.

> However if any of the typedefs in module B have leafrefs to it's own
> schema tree, you cannot deviate the entire tree as this breaks the
> contained leafref.

I don't think there's an issue here.  If a server doesn't implement
the target of a leafref in a typedef, it also cannot implement any
leaf that uses this typedef.  The typedef itself is not a problem.

/martin

> Since you cannot deviate on anything other than schema tree nodes [See
> #2] (e.g. the typedef) and module A is using an unrelated identity, this
> poses a bit of an issue (Assume you must not alter/deviate module A
> directly)
> 
> Now, this makes me think that for this to not happen, a best practice
> would be to always separate out identities, typedefs, etc.. from where
> schema trees are defined for such very cases (e.g. types modules) ....
> or introduce a method to be able to deviate non-schema tree nodes as
> such
> 
> ** ietf-interfaces is one such module where you can see the
> interface-ref/interface-state-ref dependencies back to it's own schema
> tree
> 
> For #2 - The wording around the deviation statement's target node in
> 7.20.3 specifies that this be a node in the schema tree as referenced by
> Section 6.5.  Maybe I'm missing something but I'm not seeing any
> wording around RPCs and Notifications as being part of the schema tree
> whereas other statements such as 'typedefs' are not.  As a side effect,
> this means that an RPC, Notification or top-level node in the schema
> tree cannot have the same name and must remain unique in nomenclature
> (as this is how they are each identified per their schema node
> identifier)
> 
> /ebben
> 
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