Re: [Netconf] [yang-doctors] YANG Doctor question: empty mandatory choice? (was RE: YangPush now)
Robert Wilton <rwilton@cisco.com> Fri, 27 July 2018 11:30 UTC
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To: "Eric Voit (evoit)" <evoit=40cisco.com@dmarc.ietf.org>, Kent Watsen <kwatsen@juniper.net>, "yang-doctors@ietf.org" <yang-doctors@ietf.org>
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From: Robert Wilton <rwilton@cisco.com>
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Date: Fri, 27 Jul 2018 12:30:14 +0100
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Subject: Re: [Netconf] [yang-doctors] YANG Doctor question: empty mandatory choice? (was RE: YangPush now)
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Hi Eric, Please see inline ... On 26/07/2018 20:22, Eric Voit (evoit) wrote: > > Hi YANG doctors, > > We are trying to close on some YANG push drafts. There is one YANG > related question I would like to bounce off of you before making a > suggested change. > > In the thread: > > https://www.ietf.org/mail-archive/web/netconf/current/msg15169.html > > is the following request: > > > From: Kent Watsen, July 26, 2018 1:48 PM > > > > > > <chair hat on> > > > ... > > > > > > Assuming no objections, to close the issues discussed in Montreal, > we're waiting > > > for the following updates: > > > > > > ... > > > sub-notif: modify config model to mandate a transport > > What I believe Kent is asking for is that the > ietf-subscribed-notifications.yang model should be enhanced to mandate > that transport specific call home parameters are augmented under the > container “receivers”. He wants to do this by incorporating a > mandatory choice, with no cases being identified. Cases would be > added via augmentations in subsequent drafts. > > Specifically, Kent's proposal as per > > https://www.ietf.org/mail-archive/web/netconf/current/msg15148.html > > is "to make the augmentation of a "notif" model mandatory (see the '+' > lines below), to ensure that there is always something more than just > a name being configured per receiver. > > container receivers { > > list receiver { > > key "name"; > > min-elements 1; > > leaf name { > > type string; > > } > > + choice transport { > > + mandatory true; > > + description > > + "Defines the transport-specific configuration data > > + for the selected transport."; > > + } " > > At this point there is an open question from Andy on this approach. > > https://www.ietf.org/mail-archive/web/netconf/current/msg15149.html > > Andy’s says: > > “The notion of an empty mandatory choice really stretches the > definition of YANG Conformance. This says you cannot possible > implement the SN module without some other module augmenting it. Yet > there is no way in YANG (besides import) to say the module bar needs > to be present if module foo is present.” > I can definitely get Andy's point here. I.e. that using mandatory as a conformance tool doesn't seem like a great choice. However, I think that another angle is that the configuration for a receiver a transport must always be specified. This seems like a reasonable constraint, so the mandatory also seems reasonable (regardless that it is specified as an empty choice). > My first question to you is would you object to mandatory choice > statements without corresponding case statements? If you *do* have an > issue with an empty mandatory choice, we should likely stay with the > current solution. > On balance, no I don't object. > If you see no issue with an empty mandatory choice, I have a second > question for you. For all receivers in a subscription, the selected > transport choice case in Kent’s suggestion above MUST match to the > value of the “transport” leaf which is one level higher in the tree. > I.e.: > > +--rw subscriptions > > +--rw subscription* [identifier] > > +--rw transport transport {configured}? > > +--rw receivers > > +--rw receiver* [name] > > +--rw (transport) > > +--rw :(NETCONF) > > | +--rw (NETCONF specific call home parameters) > > +--rw :(HTTP2) > > +--rw (HTTP2 specific parameters) > > (Note on the tree above, I inserted the NETCONF and HTTP2 cases of > transport for illustration purposes for the question below. These two > cases would actually be incorporated via separate augmentations to the > ietf-subscribed-notifications.yang model.) > > Considering above, It seems difficult to enforce that the transport > cases selected under all receivers for a single subscription MUST be > identical, and also MUST match to the value of the “transport” leaf > under the subscription. > As per my other email, I think that we should allow multiple transports, so the transport leaf is not required. > Would the YANG doctors have any issue with the structure Kent suggests > above? If no, would the YANG doctors then mandate that integrity > checks per performed across the receiver case instances under a > subscription? And if mandated, how might XPATH be encoded > considering transport cases are only added via augmentation? > Personally, I wouldn't mandate an xpath constraint. There are many real life constraints that are not encoded in YANG models today. If it did need to be enforced then I think that it would be an xpath expression on each transport container. Perhaps something along the lines of "the count of 'receivers' under the subscription must equal the count of '<transport-specific-container or leaf>". Thanks, Rob > Thanks, > > Eric > > > > _______________________________________________ > yang-doctors mailing list > yang-doctors@ietf.org > https://www.ietf.org/mailman/listinfo/yang-doctors
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] YANG Doctor question: empty mandato… Kent Watsen
- Re: [Netconf] YANG Doctor question: empty mandato… Andy Bierman
- Re: [Netconf] [yang-doctors] YANG Doctor question… Robert Wilton
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] YANG Doctor question: empty mandato… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Robert Wilton
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- [Netconf] YANG Doctor question: empty mandatory c… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] [yang-doctors] YANG Doctor question… Robert Wilton
- Re: [Netconf] [yang-doctors] YANG Doctor question… Robert Wilton
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] YANG Doctor question: empty mandato… Kent Watsen
- Re: [Netconf] YANG Doctor question: empty mandato… Kent Watsen
- Re: [Netconf] YANG Doctor question: empty mandato… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Juergen Schoenwaelder
- Re: [Netconf] YANG Doctor question: empty mandato… Juergen Schoenwaelder
- Re: [Netconf] YANG Doctor question: empty mandato… Alexander Clemm
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Andy Bierman
- Re: [Netconf] [yang-doctors] YANG Doctor question… Robert Wilton
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] YANG Doctor question: empty mandato… Kent Watsen
- Re: [Netconf] YANG Doctor question: empty mandato… Andy Bierman
- Re: [Netconf] YANG Doctor question: empty mandato… Einar Nilsen-Nygaard (einarnn)
- Re: [Netconf] YANG Doctor question: empty mandato… Einar Nilsen-Nygaard (einarnn)
- Re: [Netconf] YANG Doctor question: empty mandato… Henk Birkholz
- Re: [Netconf] YANG Doctor question: empty mandato… Andy Bierman
- Re: [Netconf] YANG Doctor question: empty mandato… Andy Bierman
- Re: [Netconf] YANG Doctor question: empty mandato… Kent Watsen
- Re: [Netconf] YANG Doctor question: empty mandato… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] YANG Doctor question: empty mandato… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… tom petch
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund
- Re: [Netconf] [yang-doctors] YANG Doctor question… Kent Watsen
- Re: [Netconf] [yang-doctors] YANG Doctor question… Eric Voit (evoit)
- Re: [Netconf] [yang-doctors] YANG Doctor question… Martin Bjorklund