Ladislav Lhotka <lho...@nic.cz> wrote: > On Tue, 2018-10-23 at 10:23 +0200, Martin Bjorklund wrote: > > Ladislav Lhotka <lho...@nic.cz> wrote: > > > Martin Bjorklund <m...@tail-f.com> writes: > > > > > > > > > > > Qin Wu <bill...@huawei.com> wrote: > > > > > >> -----邮件原件----- > > > > > >> 发件人: netmod [mailto:netmod-boun...@ietf.org] 代表 Ladislav Lhotka > > > > > >> 发送时间: 2018年10月22日 21:12 > > > > > >> 收件人: Martin Bjorklund > > > > > >> 抄送: netmod@ietf.org > > > > > >> 主题: Re: [netmod] xpath expressions in JSON > > > > > >> > > > > > >> On Mon, 2018-10-22 at 14:56 +0200, Martin Bjorklund wrote: > > > > > >> > Ladislav Lhotka <lho...@nic.cz> wrote: > > > > > >> > > Martin Bjorklund <m...@tail-f.com> writes: > > > > > >> > > > > > > > >> > > > Hi, > > > > > >> > > > > > > > > >> > > > Going back to the most urgent issue, what is this WG's > > > > > >> > > > recommendation for the subscribed-notifications draft in NETCONF > > > > > >> > > > wrt/ their usage of > > > > > >> > > > yang:xpath1.0 in filters? > > > > > >> > > > > > > > > >> > > > To summarize: > > > > > >> > > > > > > > > >> > > > We already have > > > > > >> > > > > > > > > >> > > > o instance-identifier in XML uses prefixes from the XML > > > >> > > > document > > > > > >> > > > o instance-identifier in JSON uses module names as prefixes > > > > > >> > > > o XPath in NETCONF filter uses prefixes from the XML document > > > > > >> > > > o XPath in JSON query filter uses module names as prefixes > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > Alternative A: > > > > > >> > > > -------------- > > > > > >> > > > > > > > > >> > > > Use different encodings for "stream-xpath-filter" as well, > > > > > >> > > > depending on if it is XML or JSON. > > > > > >> > > > > > > > > >> > > > We would do in SN: > > > > > >> > > > > > > > > >> > > > o If the node is encoded in XML, the set of namespace > > > > > >> > > > declarations are those in scope on the > > > > > >> > > > 'stream-xpath-filter' leaf element. > > > > > >> > > > > > > > > >> > > > o If the node is encoded in JSON, the set of namespace > > > > > >> > > > declarations is the set of prefix and namespace pairs > > > > > >> > > > for all supported YANG modules, where the prefix is > > > > > >> > > > > > > > >> > > Is "supported" the same as "implemented", or something else? > > > > > >> > > > > > > >> > It should be "implemented". > > > > > >> > > > > > > >> > > > the YANG module name and the namespace is as defined > > > > > >> > > > by the "namespace" statement in the YANG module. > > > > > >> > > > > > > > > >> > > > Pro: the format is consistent within each encoding. > > > > > >> > > > > > > > > >> > > > Con: unclear how to handle other encodings. > > > > > >> > > > Con: we keep using context-depending encodings. > > > > > >> > > > > > > > >> > > Con: XPath expressions in JSON can get pretty long (I assume it's > > not > > > > > >> > > just an instance identifier but may contain predicates etc.). We > > > > > >> > > cannot use the trick with the default namespace as in YANG, so > > > >> > > all > > > > > >> > > data node names will have to carry the prefix. > > > > > >> > > > > > > >> > Yes. > > > > > >> > > > > > > >> > > > We could probably add that CBOR uses the same representation as > > JSON. > > > > > >> > > > > > > > > >> > > > Example in XML: > > > > > >> > > > > > > > > >> > > > <stream-xpath-filter > > > > > >> > > > xmlns:if="urn:ietf:params:xml:ns:yang:ietf-interfaces" > > > > > >> > > > xmlns:ip="urn:ietf:params:xml:ns:yang:ietf-ip"> > > > > > >> > > > /if:interfaces/if:interface/ip:ipv4 > > > > > >> > > > </stream-xpath-filter> > > > > > >> > > > > > > > > >> > > > Example in JSON: > > > > > >> > > > > > > > > >> > > > "stream-xpath-filter": > > > > > >> > > > "/ietf-interfaces:interfaces/ietf-interfaces:interface/ietf- > > ip:ipv4" > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > Alternative B: > > > > > >> > > > -------------- > > > > > >> > > > > > > > > >> > > > Use a non-context depending encoding, with the module name as > > prefix. > > > > > >> > > > > > > > > >> > > > We would do in SN: > > > > > >> > > > > > > > > >> > > > o The set of namespace > > > > > >> > > > declarations is the set of prefix and namespace pairs > > > > > >> > > > for all supported YANG modules, where the prefix is > > > > > >> > > > the YANG module name and the namespace is as defined > > > > > >> > > > by the "namespace" statement in the YANG module. > > > > > >> > > > > > > > > >> > > > Pro: the format is independent from the protocol encoding > > > > > >> > > > > > > > > >> > > > Con: in XML, this leaf is treated differently from other XPath > > > > > >> > > > expressions, such as get-config filter and nacm rules. > > > > > >> > > > > > > > > >> > > > Example in XML: > > > > > >> > > > > > > > > >> > > > <stream-xpath-filter> > > > > > >> > > > /ietf-interfaces:interfaces/ietf-interfaces:interface/ietf- > > ip:ipv4 > > > > > >> > > > </stream-xpath-filter> > > > > > >> > > > > > > > > >> > > > Example in JSON: > > > > > >> > > > > > > > > >> > > > "stream-xpath-filter": > > > > > >> > > > "/ietf-interfaces:interfaces/ietf-interfaces:interface/ietf- > > ip:ipv4" > > > > > >> > > > > > > > > >> > > > > > > > > >> > > > My proposal is A. I think it is more important with consistency > > > > > >> > > > within each encoding than across encodings. > > > > > >> > > > > > > > >> > > I would suggest to consider declaring prefixes & namespaces > > > > > >> > > explicitly in the data, as in the schema mount document. It is > > > > > >> > > independent of encoding and the expressions can be kept short. In > > > > > >> > > fact, one of the namespaces can be declared as default, so this > > > >> > > use > > > > > >> > > of XPath would then be very similar to YANG. > > > > > >> > > > > > > >> > Ok, so this is another alternative that works today, and achieves > > > >> > the > > > > > >> > goal of being encoding-independent. It is still context-dependent > > > > > >> > though. > > > > > >> > > > > > >> Yes, every module that uses XPath in data will have to deal with this. > > There may potentially be multiple independent prefix declarations (this is > > actually a con). > > > > > >> > > > > > >> > > > > > > >> > BTW, when used in filters, it is nice to let an unprefixed name to > > > > > >> > match any namespace; i.e., treat "foo" as syntactic sugar for > > > > > >> > "local-name(.) = 'foo'". ("*:foo" is not legal...) > > > > > >> > > > > > >> Hmm, I think this is a bad idea because it departs even further from > > > >> the > > original XPath semantics. Such chameleon names should IMO be pretty rare, > > and > > if they are needed, local-name() is always available. > > > > > >> > > > > > >> [Qin]: Agree with Lada, Referencing RFC8407, section 4.6.2, I think the > > below guideline is relevant. > > > > > >> " > > > > > >> The "local-name" function SHOULD NOT be used to reference local names > > > > > >> outside of the YANG module that defines the must or when expression > > > > > >> containing the "local-name" function. Example of a "local-name" > > > > > >> function that should not be used: > > > > > >> > > > > > >> /*[local-name()='foo'] > > > > > > > > > > > > This guideline is for must/when expressions *within* YANG modules. > > > > > > > > > > > > I'm talking about a different use case, namely filtering. It is > > > > > > pretty convenient for users to send a filter: > > > > > > > > > > > > /interfaces/interface[name='eth0'/ipv4 > > > > > > > > > > This is impossible if we want to call it XPath. With an explicit > > > > > namespace/prefix declaration, for example > > > > > > > > > > "namespace": [ > > > > > { > > > > > "prefix": "if", > > > > > "uri": "urn:ietf:params:xml:ns:yang:ietf-interfaces", > > > > > "default": true > > > > > }, > > > > > { > > > > > "prefix": "ip", > > > > > "uri": "urn:ietf:params:xml:ns:yang:ietf-ip" > > > > > } > > > > > ] > > > > > > > > > > it would be > > > > > > > > > > /interfaces/interface[name='eth0']/ip:ipv4 > > > > > > > > > > which is not too bad either. > > > > > > Well, "ncc myhost --get -x /interfaces/interface[name='eth0']/ipv4" is > > a one-liner; if I also have to specify the namespace list for every > > filter, it suddenly is not that convenient. > > But this is an UI issue. I am not against any aid provided by client tools, > what > I am talking about is the "oficial" lexical representation of that data type, > that is also exchanged in protocols.
> The above expression breaks XPath rules. This I agree with! /martin _______________________________________________ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod
