Re: [YANG] default values

If we could agree that a leaf thats set automatically to it's default at least conceptually 
exists, that would make understanding how this works MUCH easier.
However we have to describe how this effects non-presence containers
Balazs

Martin Bjorklund wrote:
> Phil Shafer <phil@juniper.net> wrote:
>> Balazs Lengyel writes:
> 
>>> One more thing I think is still missing from the draft, is whether
>>> must expressions consider default values or not?
>> We discussed this at some point and decided that "must"s must
>> see defaults, but there needs to be a helper function to allow
>> one to detect unconfigured values.
>>
>>     must "../mtu < 1500 or not(yang:is-set(../mtu))";
>>
>> I don't think this is in the current spec.
> 
> It's on my TODO list.
> 
> I was thinking the text should say that default values exist in the
> data tree, and then clarify the text about XML encoding of leafs to
> say that leafs which are set to their default values in the data tree
> do not have to be sent.  The must description talks about the data
> tree, so by adding the defaults to the data tree, the must expressions
> are covered.
> 
> One question is how the xpath function should behave:
> 
>                             node set     node set to   node does
>                             to default   other value   not exist
>    --------------------------------------------------------------
>    yang:has-default(node)    true          false         false
>    yang:is-set(node)         false         true          false
> 
> 
> Maybe it's no big deal - if you want to check for existance, that's
> trivial in XPath.
> 
> 
> /martin

-- 
Balazs Lengyel                       Ericsson Hungary Ltd.
TSP System Manager
ECN: 831 7320                        Fax: +36 1 4377792
Tel: +36-1-437-7320     email: Balazs.Lengyel@ericsson.com

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