[Nsi-wg] Modify behaviors

[Hans Trompert]

On 21/12/15 19:41, John MacAuley wrote:
>
> Hans and I have been working through behaviours of the Modify
> operation as the NSI CS document is a little vague on some of the more
> detailed aspects of the operation.  Our most recent discussion focused
> on the modification of startTime.  For example, let us say reservation
> X has a startTime of "now + 1 hour", but I would like to modify the
> startTime to start "now".
>
> In an initial reservation request we specify at startTime of now by
> omitting the <startTime> element, however, for a modify operation we
> cannot distinguish from a startTime not specified for modification and
> the startTime intentionally missing to indicate "now".
>
> In the current schema definition we cannot use an empty <startTime>
> element as it is an illegal xsd:dateTime.  So that only leaves us with
> the option of specifying a <startTime> reasonably close to now, but
> well all now how troublesome this is with our current implementations.

Exactly, that was the reason why we came up with the possibility to
leave startTime or endTime empty to specify 'start now' and 'last
forever' reservations. I don't look forward to implement all kind of
workarounds again.

> There is a solution to this issue.  If we modify the existing schema
> to allow for the "nillable" option on startTime we can now specify an
> empty <startTime xsi:nil="true" /> element to handle this "start time
> of now" case.  This would require a non-backwards compatible change
> for modify, but I am not sure how may NSA implementations of modify exist.

It is not because I proposed this of course ;-), but I believe this is
the best solution to modify start or end time without having to change
the current semantics around startTime and endTime.

> The second issue is what happens if in the modify request a parameter
> with the same value is provided?  Do we fail the modify or continue
> with the same value?  For example, if a modify is received with the
> same startTime but a different endTime do we reject to modify since it
> contains the same startTime, or do we accept the modify and only
> change the endTime?
>
> I would assume we accept the modify operation an proceed with
> modification of endTime.  What happens if only one parameter, say
> capacity, is specified and it contains the same value as the current
> reservation version?

Seen from a practical perspective, you already have to keep track of the
current reservation details to implement idempotency, so it is very easy
to check if a value specified in a modify is different from the current
value, only question is what are you going to do after that, are you
going send back an error or are you just going to accept it as a no-op.

Related to this, is it allowed to send a modify that does not change any
of parameters of the reservation? And will that then result in a new
reservation with a higher criteria version?

Cheers,
    HansT.
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