Re: [netmod] Constraining instance-identifiers

[Balazs Lengyel]

Hello, I agree we don't need to change the encoding, but we need to define how that encoding is visible/available when evaluating Xpath expressions. Today the draft says: - instance-identifier does not have a canonical format - XPath uses the canonical format The two together make it impossible to use it in Xpath, even though there are people that would like to do that. - Martin mentioned a proprietary extension - we would like it. So I would propose to ---- change to 9.1 Old: In particular, any XPath _expression_ evaluations are done using the canonical form. New:  In particular, whenever a canonical form exists, any XPath _expression_ evaluations are done using the canonical form. --- add to 9.13.2 For instance-identifiers XPath _expression_ evaluations are done using the lexical form. regards Balazs On 2016-01-21 18:53, Andy Bierman wrote: Hi, There is no need to change the XML encoding or YANG encoding of an instance-identifier.  The prefixes are completely different in each.  Prefixes clashes do happen, especially since there is no expectation that they are unique.  They are short strings with no naming conventions at all.  E.g., I have seen "if" for interfaces in multiple modules. Andy On Thu, Jan 21, 2016 at 8:51 AM, Balazs Lengyel <balazs.leng...@ericsson.com> wrote: Hello Martin, If the RFC would define that in XPath expressions an instance identifier MUST be evaluated to a string that complies to the lexical format, using the rematch function, we could do everything we need. In real life prefix clashes are a rare problem. regards Balazs On 2016-01-21 16:17, Martin Bjorklund wrote: Balazs Lengyel <balazs.leng...@ericsson.com> wrote: Hello, We have some instance identifiers in our model but we want to contrain what they can point at. What is the best method for that? Unfortunately, there is no standard way of doing this.  (There are vendor extensions available...) [...] Some issues: - instance-identifiers don't have a canonical format, so what is their value in an XPath _expression_? This is not defined. - I didn't find a way to evaluate a regexp in XPath 1.0. Is there a way? In YANG 1.1, there is a function re-match() for this purpose.  For your use case, it *may* work to match just the local names of all nodes, i.e., using wildcards for the prefixes.  It is not a generic solution though. - if I have all the needed namespace prefixes in imports, can I just    use them? No, these prefixes are local to the module that is doing the import, and they may or may not match the prefixes used by the implementation when it construct the instance-identifier value. /martin -- Balazs Lengyel                       Ericsson Hungary Ltd. Senior Specialist ECN: 831 7320 Mobile: +36-70-330-7909              email: balazs.leng...@ericsson.com _______________________________________________ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod -- Balazs Lengyel Ericsson Hungary Ltd. Senior Specialist ECN: 831 7320 Mobile: +36-70-330-7909 email: balazs.leng...@ericsson.com

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