"Dale R. Worley" <wor...@ariadne.com> writes: > Andy Bierman <a...@yumaworks.com> writes: >> Using a key of type empty is utterly pointless unless the point >> is to make the instance identifier longer. > > IMO using a key of type empty (or any type with only one value) is > *pointless* but should be *valid*. Things should be valid unless > processing them according to the ordinary rules can't work. Indeed, > specifically banning them increases the complexity of the > specification.
+1 There is no need to ban keys with type "empty", XPath and everything works fine if other YANG rules are followed. Lada > > The reason for this is that the code (in this case, the module > definition) may be generated by an automatic process, and those > processes are easier to construct if the rules contain fewer > irregularities. E.g., multiplying a number by zero is pointless, in > that the result is always zero, and one might ask, Why not just write 0 > instead of the multiplication? But everyone agrees that the statement > > a = 0 * b; > > is *valid*, and can easily imagine situations where a process might > generate it as an output. > >>> Unless I'm off, the line should be fixed to avoid the string >>> conversion: >>> >>> /ex:system/ex:service[ex:name='foo'][ex:enabled] >>> >>> and a negation should be: >>> >>> /ex:system/ex:service[ex:name='foo'][not(ex:enabled)] >> >> There is only one value provided by type empty. The 2nd instance >> identifier is invalid. >> There is no instance possible that does not include the 'enabled' leaf. > > The 2nd instance identifier is (should be) *valid* even if it always > returns the empty set. (Assuming it is used in contexts where a set can > be returned.) > > Dale > > _______________________________________________ > netmod mailing list > netmod@ietf.org > https://www.ietf.org/mailman/listinfo/netmod -- Ladislav Lhotka, CZ.NIC Labs PGP Key ID: E74E8C0C _______________________________________________ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod
