Juergen Schoenwaelder <j.schoenwael...@jacobs-university.de> writes: > On Wed, Sep 16, 2015 at 08:29:16PM +0200, Ladislav Lhotka wrote: >> >> > On 16 Sep 2015, at 18:00, Andy Bierman <a...@yumaworks.com> wrote: >> > >> > >> > >> > On Wed, Sep 16, 2015 at 8:17 AM, Juergen Schoenwaelder >> > <j.schoenwael...@jacobs-university.de> wrote: >> > On Tue, Sep 15, 2015 at 12:21:44PM -0700, Andy Bierman wrote: >> > > On Tue, Sep 15, 2015 at 12:01 PM, Randy Presuhn < >> > > randy_pres...@mindspring.com> wrote: >> > > >> > > > Hi - >> > > > >> > > > >From: Juergen Schoenwaelder <j.schoenwael...@jacobs-university.de> >> > > > >Sent: Sep 14, 2015 11:41 PM >> > > > >To: Ladislav Lhotka <lho...@nic.cz> >> > > > >Cc: NETMOD Working Group <netmod@ietf.org> >> > > > >Subject: Re: [netmod] Fwd: New Version Notification for >> > > > draft-ietf-netmod-yang-json-05.txt >> > > > ... >> > > > >My question is why the text is silent about the case where the data >> > > > >model is present. Should it not say that if the data model is present, >> > > > >the data encoded inside the anydata node must follow the rules of this >> > > > >document? Perhaps this is the implicit assumption but I think it will >> > > > >be useful to say this explicitly (if we agree on this). >> > > > > >> > > > >If the data model is not present, then I think an implementation is >> > > > >still expected to produce an encoding that follows the rules of this >> > > > >document as much as possible except that things that requires data >> > > > >model knowledge may be encoded differently (e.g., numbers appearing as >> > > > >strings or namespace names being different). I am thinking along the >> > > > >lines of this proposed new text: >> > > > > >> > > > > An anydata data node can contain an unknown set of nodes that can >> > > > > be modelled by YANG. A data model for anydata content may or may >> > > > > not exist at run time. If the data model for anydata content is >> > > > > available, then the anydata content MUST be encoded according to >> > > > > the rules of this specification. If the data model for anydata >> > > > > content is not available, the encoding MUST follow the rules of >> > > > > this specification except for rules that require data model >> > > > > knowledge (and as a consequence, numbers may appear as strings or >> > > > > namespace qualifiers may not match module names). >> > > > >> > > > This leaves me wondering what it means for the data model for >> > > > anydata content to be "available". In the case of ASN.1's >> > > > "ANY DEFINED BY" construct, there's an OBJECT IDENTIFIER to >> > > > unambiguously identify the grammar (and associated semantics) >> > > > to be used to understand the content, so tools can, if needed, >> > > > scurry off to obtain the parsing instructions for those >> > > > particular bits. How does an implementation know in the case >> > > > of "anydata" which datamodel to use? >> > > > >> > > > >> > > Good questions.... >> > > The text "If the data model for anydata content is available" gives a >> > > hint >> > > of just >> > > what a hack anydata is in YANG. The definition of anydata is that there >> > > is >> > > no data model for the specified subtree. The mere mention of an >> > > out-of-band >> > > data mode is inappropriate and confusing. >> > > >> > > I understand this is intended to support usage like in YANG Patch, where >> > > the >> > > description-stmt of 'value' says that the child node must follow the >> > > schema >> > > for the node in the target leaf. More hacks to get YANG to work. >> > >> > You are welcome to provide fixes. >> > >> > >> > OLD: >> > >> > >> > An anydata data node can contain an unknown set of nodes that can >> > be modelled by YANG. A data model for anydata content may or may >> > not exist at run time. If the data model for anydata content is >> > available, then the anydata content MUST be encoded according to >> > the rules of this specification. If the data model for anydata >> > content is not available, the encoding MUST follow the rules of >> > this specification except for rules that require data model >> > knowledge (and as a consequence, numbers may appear as strings or >> > namespace qualifiers may not match module names). >> > >> > >> > NEW: >> > >> > An anydata data node can contain an unknown set of nodes that can >> > be modelled by YANG. >> >> This text is essentially in 6020bis, I see no need to repeat it. >> >> > >> > >> > The YANG RFC itself should be silent about data-model specific >> > semantics that are added to an anydata subtree. The text "if available" >> > is especially non-enforceable and therefore pointless. >> > >> >> I must admit I am getting lost in these discussions. It seems to me there is >> a lot of hand-waving and hidden assumptions that moreover differ from one >> person to another. As I already said in Prague, both anyxml and anydata are >> IMO constructs of marginal utility and it is frustrating we spend so much >> effort on them. >> > > I agree that anyxml is of marginal utility, anydata however is needed > for any rpc/action/notification or future language construct that can > work with generic YANG content and hence I think its behaviour and > encoding should be well defined.
But then I believe we should have stricter rules for anydata than just "an unknown set of nodes that can be modelled with YANG" - it should be stated that the data model for an anydata instance MUST be known at run-time. Otherwise I think anyxml can cover all use cases you mention as well (as it has done in the past), and there is no need to introduce a new data node type with a definition that allows for multiple interpretations. Lada > > /js > > -- > Juergen Schoenwaelder Jacobs University Bremen gGmbH > Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany > Fax: +49 421 200 3103 <http://www.jacobs-university.de/> -- Ladislav Lhotka, CZ.NIC Labs PGP Key ID: E74E8C0C _______________________________________________ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod
