On Wed, Oct 10, 2018 at 11:44 AM, Michael Rehder <michael.reh...@amdocs.com> wrote:
> Sure. > > I think the RFC is unclear since it seems that the semantics are > consistent in the back-end checks. > One can read the RFC and not notice by its absence that the when clause > doesn't require anything to be present. > > The "when" statement makes its parent data definition statement > conditional. > Should be > The "when" statement makes its parent data definition statement > conditional and optional. > > This is not correct. Step 1) if-feature makes the schema node conditional Step 2) when-stmt makes instances of the schema-node conditional Step 3) YANG validation applies to instances of data nodes (or the YANG default value if applicable) Step 2 is only relevant if Step 1 is true or non-existent Step 3 is only relevant if Step 2 is true or non-existent Andy > I think there should be a more definite statement about this overriding > any mandatory status of the parent data definition statement. > Like > "Any mandatory status of the parent data definition statement > (mandatory statement, min-element statement etc.) is overridden by this > statement and made non-mandatory." > > That would have made the side-effect of "when" on other declarations > clearer. > > Thanks > mike > > -----Original Message----- > > From: Juergen Schoenwaelder [mailto:j.schoenwael...@jacobs-university.de > ] > > Sent: Wednesday, October 10, 2018 2:25 PM > > To: Michael Rehder <michael.reh...@amdocs.com> > > Cc: Robert Wilton <rwil...@cisco.com>; Ladislav Lhotka <lho...@nic.cz>; > > netmod@ietf.org; Walker, Jason (jason_walk...@comcast.com) > > <jason_walk...@comcast.com> > > Subject: Re: [netmod] WHEN statement within mandatory objects doesn't > > ensure presence of the mandatory object > > > > 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:rwil...@cisco.com] > > > > Sent: Wednesday, October 10, 2018 11:33 AM > > > > To: Michael Rehder <michael.reh...@amdocs.com>; Ladislav Lhotka > > > > <lho...@nic.cz>; netmod@ietf.org > > > > Cc: Walker, Jason (jason_walk...@comcast.com) > > > > <jason_walk...@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:lho...@nic.cz] > > > > >> Sent: Wednesday, October 10, 2018 10:28 AM > > > > >> To: Michael Rehder <michael.reh...@amdocs.com>; netmod@ietf.org > > > > >> Subject: Re: [netmod] WHEN statement within mandatory objects > > > > >> doesn't ensure presence of the mandatory object > > > > >> > > > > >> Michael Rehder <michael.reh...@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.htm > > > > >> l > > > > >> > > > > >> 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/> > “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 >
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