Re: [netmod] WHEN statement within mandatory objects doesn't ensure presence of the mandatory object
Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> Wed, 10 October 2018 18:25 UTC
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Date: Wed, 10 Oct 2018 20:25:29 +0200
From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>
To: Michael Rehder <Michael.Rehder@Amdocs.com>
CC: Robert Wilton <rwilton@cisco.com>, Ladislav Lhotka <lhotka@nic.cz>, "netmod@ietf.org" <netmod@ietf.org>, "Walker, Jason (Jason_Walker2@comcast.com)" <Jason_Walker2@comcast.com>
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Subject: Re: [netmod] WHEN statement within mandatory objects doesn't ensure presence of the mandatory object
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Michael, what matters here is what the YANG specification (RFC 7950) says. Is there a reason to believe the IPAddresses list in your example can be absent or have no elements based on what RFC 7950 says? Or do we talk about a shortcoming of RFC 6110? /js On Wed, Oct 10, 2018 at 06:17:26PM +0000, Michael Rehder wrote: > If the list has a "when" clause the RNG file actually produces a "OneOrMore" which has a choice of <empty> or the list so it actually doesn't enforce the presence at least one row of the list (unless I'm mistaken in my reading). > <oneOrMore> > <choice> > <empty/> > <element name="IPAddresses"> > <element name="Address"> > <ref name="types__IPv4Address"/> > </element> > <empty/> > </element> > </choice> > </oneOrMore> > > A leaf/container would be a simpler example but would result in the same lack of enforcement of the mandatory status of an element with a "when" clause. > > This RNG seems consistent with the Schematron rules that "when" makes something optional. > > > I think a workaround would be choice with mandatory true and a when clause on the cases. This would ensure that at least one case is present since the mandatory clause implements a Schematron existence constraint. > > Thanks > Mike > > -----Original Message----- > > From: Robert Wilton [mailto:rwilton@cisco.com] > > Sent: Wednesday, October 10, 2018 11:33 AM > > To: Michael Rehder <Michael.Rehder@Amdocs.com>; Ladislav Lhotka > > <lhotka@nic.cz>; netmod@ietf.org > > Cc: Walker, Jason (Jason_Walker2@comcast.com) > > <Jason_Walker2@comcast.com> > > Subject: Re: [netmod] WHEN statement within mandatory objects doesn't > > ensure presence of the mandatory object > > > > Hi Mike, > > > > I think that the YANG below already enforces what you want, or otherwise I > > don't follow your issue. > > > > The YANG below is valid in two cases: > > > > (1) AssignmentMechanism = DHCP, and IPAddresses is not present in the config > > (due to the when statement). > > (2) AssignmentMechanism = Static, IPAddresses exists and has at least one > > element (due to min-elements 1). > > > > Thanks, > > Rob > > > > > > On 10/10/2018 16:23, Michael Rehder wrote: > > > Container "foo" would be mandatory if not for the "when" child element. > > > With the "when" child element, the logic becomes "inverted" and the > > constraint is a negative one of "disallowed under certain condition". > > > > > > The UC is for enforcement in REST API payloads. > > > For a practical example: > > > > > > leaf AssignmentMechanism { > > > type enumeration { > > > enum "DHCP"; > > > enum "Static"; > > > } > > > mandatory true; > > > description "The address assignment mechanism."; > > > } > > > list IPAddresses { > > > when "../AssignmentMechanism = 'Static'"; > > > key Address; > > > min-elements 1; > > > > > > leaf Address { > > > type capit:IPv4Address; > > > description "An ipv4 address."; > > > } > > > } > > > > > > There is no way in the IPAddresses list to enforce that there is at least one IP > > Address when the assignment method is "Static". > > > One could put a "must" on "AssignmentMechanism" to ensure at least one > > element of the IPAddresses list when "Static", but I don't see this as a good > > schema design, to have the controlling attribute check controlled attributes. > > > > > > I appreciate that this semantic can't be changed in YANG at this point. > > > Could the "when" statement have a modifying child element to state that the > > mandatory status of the element is to be enforced? > > > Like > > > container foo { > > > when "condition" { > > > enforce-mandatory-status; > > > } > > > > > > There is already back-end for existential checks for mandatory choice so this > > seems reasonably consistent to me. > > > I appreciate there are existing issues for "when" but I don't see why this > > would make things any worse. > > > In fact by promoting a better dependency "direction" between schema > > elements, think it could simplify things (so I naively think :) ). > > > > > > Thanks > > > Mike > > >> -----Original Message----- > > >> From: Ladislav Lhotka [mailto:lhotka@nic.cz] > > >> Sent: Wednesday, October 10, 2018 10:28 AM > > >> To: Michael Rehder <Michael.Rehder@Amdocs.com>; netmod@ietf.org > > >> Subject: Re: [netmod] WHEN statement within mandatory objects doesn't > > >> ensure presence of the mandatory object > > >> > > >> Michael Rehder <Michael.Rehder@Amdocs.com> writes: > > >> > > >>> I have a question about “when” and mandatory objects. > > >>> > > >>> It seems to me that the implemented semantics of “when” are really > > >> “optional when”, in that the enclosing object can be absent even > > >> though it is mandatory and the “when” clause holds true. > > >>> The RFC could be clearer about this. > > >>> > > >>> Example > > >>> > > >>> leaf color { > > >>> enumeration { > > >>> enum “blue”; > > >>> enum “black”; > > >>> } > > >>> mandatory true; > > >>> } > > >>> container foo { > > >>> when ../color = ‘blue’; > > >>> etc. > > >>> } > > >>> > > >>> “foo” is optional due to the presence of the “when” statement even > > >>> though the object is mandatory (same is true for mandatory leaf, > > >>> min-elements=1 list etc.). > > >> Maybe you intended to have, e.g., a "mandatory true" leaf inside > > >> "container foo"? > > >> > > >>> This is considered valid XML for the above > > >>> <color>blue</color> > > >> Yes, it is, under current YANG rules, no matter what "etc." stands > > >> for. Note that evaluation of the XPath expression in this case (with > > >> "foo" missing) requires the peculiar procedure of sec. 7.21.5 in RFC 7950. > > >> > > >>> In my view this makes conditionally variant schemas “loose” in their > > >>> enforcement (some scenarios can use choice but it doesn’t cover > > >>> everything). > > >>> > > >>> I think that mandatory should be respected for the enclosing objects > > >>> of a “when” statement. That is, a mandatory object must be present > > >>> when its “when” clause holds true and a Schematron statement should > > >>> enforce that. > > >> In fact, this is one case where the DSDL mapping (RFC 6110) deviates > > >> from YANG 1.0. Nodes that mandatory aren't enclosed in the RELAX NG > > >> <optional> pattern, and are then required no matter what any "when" > > >> statements say (because RELAX NG validation comes before Schematron). > > >> > > >>> What is the rationale behind the current YANG rules behavior, that > > >>> the “when” Schematron mapping doesn’t check for presence of the > > >>> enclosing mandatory object? > > >> FWIW, I have been repeatedly protesting against this behaviour but > > >> without much luck. See for example > > >> > > >> https://www.ietf.org/mail-archive/web/netmod/current/msg14012.html > > >> > > >> As a result, "when" is the trickiest feature in YANG by far. > > >> > > >> Lada > > >> > > >>> thanks > > >>> Mike Rehder > > >> -- > > >> Ladislav Lhotka > > >> Head, CZ.NIC Labs > > >> PGP Key ID: 0xB8F92B08A9F76C67 > > > “Amdocs’ email platform is based on a third-party, worldwide, cloud-based > > system. Any emails sent to Amdocs will be processed and stored using such > > system and are accessible by third party providers of such system on a limited > > basis. Your sending of emails to Amdocs evidences your consent to the use of > > such system and such processing, storing and access”. > > > _______________________________________________ > > > netmod mailing list > > > netmod@ietf.org > > > https://www.ietf.org/mailman/listinfo/netmod > > “Amdocs’ email platform is based on a third-party, worldwide, cloud-based system. Any emails sent to Amdocs will be processed and stored using such system and are accessible by third party providers of such system on a limited basis. Your sending of emails to Amdocs evidences your consent to the use of such system and such processing, storing and access”. > _______________________________________________ > netmod mailing list > netmod@ietf.org > https://www.ietf.org/mailman/listinfo/netmod -- Juergen Schoenwaelder Jacobs University Bremen gGmbH Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany Fax: +49 421 200 3103 <https://www.jacobs-university.de/>
- [netmod] WHEN statement within mandatory objects … Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Sterne, Jason (Nokia - CA/Ottawa)
- Re: [netmod] WHEN statement within mandatory obje… Ladislav Lhotka
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Robert Wilton
- Re: [netmod] WHEN statement within mandatory obje… Ladislav Lhotka
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Juergen Schoenwaelder
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Ladislav Lhotka
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Robert Wilton
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Robert Wilton
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Juergen Schoenwaelder
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Robert Wilton
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Robert Wilton
- Re: [netmod] WHEN statement within mandatory obje… Ladislav Lhotka
- Re: [netmod] WHEN statement within mandatory obje… Michael Rehder
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Alex Campbell
- Re: [netmod] WHEN statement within mandatory obje… Andy Bierman
- Re: [netmod] WHEN statement within mandatory obje… Alex Campbell