Dear Sudhanshu, I share Robert's concerns. Hard coding expressions in a syntax tree format in a schema is hardly readable and highly inflexible. Note that there has been prior work like this in different contexts and one thing you entirely ignore is that management data is not static; counter leaf values have no meaning unless you compute a delta over a time period etc.
You also seem to confuse basic concepts, i.e., protocols like NETCONF do not parse schema definitions. So why would NETCONF need enhancements? It should be a design goal to not require protocol enhancements. /js On Fri, Sep 29, 2017 at 12:57:54PM +0000, Sudhanshu Kumar Srivastav wrote: > Hi Robert, > > > > Please find response inline. > > > > 1) In particular, rather than modeling the expression directly in YANG > using YANG extensions, which effectively makes the expression look like > quite a verbose abstract syntax tree, I think that you may be better off > defining a separate expression language, similar to how Xpath is used > today. Probably it could be related to Xpath, perhaps it could be a > superset. > > [srivastav] There is slight difference in suggested idea and > that is "Model the formula as schema, not as Data". > > > > 2) I think that there are some questions about how these expressions would > get programmed into the device. Are they statically included as part of > the schema loaded by the NETCONF/RESTCONF server? Or are they programmed > dynamically via the NETCONF/RESTCONF client. For the latter case it would > be necessary to either define new RPC operations, or perhaps better a > configuration and operational YANG data model to manage the expressions. > > [srivastav] formulas are getting statically included at server and not > programmed dynamically. The benefit of this is when formula changes, Just > schema need to be changed and updated at server and no change in server is > required. > > > > 3) I think that it would also need to be considered whether the > constructed expression values are represented as new nodes in the YANG > schema (which would probably prevent them from be constructed > dynamically), or perhaps they should make use of YANG metadata (RFC 7952) > instead so that the base underlying schema isn't changed. > > [srivastav] YANG metadata (RFC 7952) shall be used. > > 4) Any solution should probably also consider how it would inter-operate > with the work currently being doing in NETCONF on YANG push and related > technologies. > [srivastav] I don't foresee any inter-operability problem with YANG push > technology. Kindly let me know if you foresee any problem. > > 5) They may be security implications of allowing a client to execute > arbitrarily complex expressions would may degrade the performance of the > system, although perhaps the memory and cpu available to execute the > expressions could be limited. > > [srivastav] Modeling formula as schema don't put this security > implications, as formula is not getting programmed dynamically. > > > > > > Kindly let me know how can I proceed further to this idea from > conceptualization to realization in IETF forum. > > > > Regards > > Sudhanshu > > > > --------- Original Message --------- > > Sender : Sudhanshu Kumar Srivastav <[email protected]> Chief > Engineer/SRI-Bangalore-CU/Samsung Electronics > > Date : 2017-09-15 19:58 (GMT+5:30) > > Title : RE: Re: [netmod] draft-srivastav-netmod-formulae-00 > > To : null<[email protected]>, null<[email protected]> > > CC : KARTHIKEYAN SUBRAMANIAM<[email protected]>, cpgs > .<[email protected]>, Surendra Pal Sharma<[email protected]> > > > > Dear Robert, > > > > Thanks a lot for your feedback. It gave me other key areas to be > considered which can be impacted due to the suggested idea. > > > > With respect to first feedback, I think there is slight difference > in suggested idea and that is "Model the formula as schema, not as > Data". So it's getting statically included at server and not programmed > dynamically. > > As I think "Modeling formula" as Data may have security implications. > > > > I am going through the feedbacks provided in details, I will check and > come back to this. > > > > Regards > > Sudhanshu > > > > --------- Original Message --------- > > Sender : Robert Wilton <[email protected]> > > Date : 2017-09-13 15:11 (GMT+5:30) > > Title : Re: [netmod] draft-srivastav-netmod-formulae-00 > > To : Sudhanshu Kumar Srivastav<[email protected]>, > null<[email protected]> > > CC : KARTHIKEYAN SUBRAMANIAM<[email protected]>, cpgs > .<[email protected]> > > > > Hi Sudhanshu, > > Thanks for posting this. > > The premise of what you are trying to achieve here is interesting. My > interpretation is that your idea is to allow a NETCONF/RESTCONF > server/device to take existing data in the operational state data tree and > to construct new derived data (or perhaps just metadata) by executing a > client defined algorithm that is described via extensions statements to > YANG. > > This broadly seems a reasonable idea to me, but I'm not sure that I would > implement it in quite the same way, and I've put forward some other points > or issues that you may want to consider. > > 1) In particular, rather than modeling the expression directly in YANG > using YANG extensions, which effectively makes the expression look like > quite a verbose abstract syntax tree, I think that you may be better off > defining a separate expression language, similar to how Xpath is used > today. Probably it could be related to Xpath, perhaps it could be a > superset. > > E.g .to take your example in 3.10, I think that it would be better if the > expression was written more like a normal mathematical expression. E.g. I > think that the following would be easier to read/understand. Obviously an > implementation needs to parse the expression, but that shouldn't be too > difficult, and they would need to write code to interpret the expression > anyway. > > container formula { > leaf a { > type int32; > } > ... leaves b to d defined similarly ... > leaf e { > type int32; > } > mt:math x { > leaf x { > type int32; > mt:expression"((a+b) - (c-d)/(e*100))"; > } > } > > 2) I think that there are some questions about how these expressions would > get programmed into the device. Are they statically included as part of > the schema loaded by the NETCONF/RESTCONF server? Or are they programmed > dynamically via the NETCONF/RESTCONF client. For the latter case it would > be necessary to either define new RPC operations, or perhaps better a > configuration and operational YANG data model to manage the expressions. > > 3) I think that it would also need to be considered whether the > constructed expression values are represented as new nodes in the YANG > schema (which would probably prevent them from be constructed > dynamically), or perhaps they should make use of YANG metadata (RFC 7952) > instead so that the base underlying schema isn't changed. > > 4) Any solution should probably also consider how it would inter-operate > with the work currently being doing in NETCONF on YANG push and related > technologies. > > 5) They may be security implications of allowing a client to execute > arbitrarily complex expressions would may degrade the performance of the > system, although perhaps the memory and cpu available to execute the > expressions could be limited. > > I hope the brief feedback is useful. I'm not sure how familiar you are > with the IETF process, but please note that these comments just represent > my personal opinion and do not necessarily reflect those of the wider > participants in the NETMOD WG. Other opinions may, and in my experience > probably will, differ :-) > > Thanks, > Rob > > On 13/09/2017 08:30, Sudhanshu Kumar Srivastav wrote: > > Dear NETMOD Team, > > > > I have submitted a draft for new YANG module that defines new YANG > extension statements and method to model the formulae/KPI's. > > Request you to please check and provide your comments. > > > > Draft Details: > > Name: draft-srivastav-netmod-formulae > Revision: 00 > Title: YANG extension Statements for formulae modeling > Document date: 2017-09-12 > Group: Individual Submission > Pages: 28 > URL: > > [1]https://www.ietf.org/internet-drafts/draft-srivastav-netmod-formulae-00.txt > Status: > [2]https://datatracker.ietf.org/doc/draft-srivastav-netmod-formulae/ > Htmlized: > [3]https://tools.ietf.org/html/draft-srivastav-netmod-formulae-00 > Htmlized: > > [4]https://datatracker.ietf.org/doc/html/draft-srivastav-netmod-formulae-00 > > > > Regards > > Sudhanshu > > _______________________________________________ > netmod mailing list > [5][email protected] > [6]https://www.ietf.org/mailman/listinfo/netmod > > > > References > > Visible links > 1. > https://www.ietf.org/internet-drafts/draft-srivastav-netmod-formulae-00.txt > 2. https://datatracker.ietf.org/doc/draft-srivastav-netmod-formulae/ > 3. https://tools.ietf.org/html/draft-srivastav-netmod-formulae-00 > 4. https://datatracker.ietf.org/doc/html/draft-srivastav-netmod-formulae-00 > 5. mailto:[email protected] > 6. https://www.ietf.org/mailman/listinfo/netmod > _______________________________________________ > netmod mailing list > [email protected] > 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 <http://www.jacobs-university.de/> _______________________________________________ netmod mailing list [email protected] https://www.ietf.org/mailman/listinfo/netmod
