IRC log of swd on 2007-12-04
Timestamps are in UTC.
- 15:59:40 [RRSAgent]
- RRSAgent has joined #swd
- 15:59:40 [RRSAgent]
- logging to http://www.w3.org/2007/12/04-swd-irc
- 15:59:44 [Zakim]
- Zakim has joined #swd
- 16:00:02 [Simone]
- Simone has joined #swd
- 16:00:42 [edsu]
- edsu has joined #swd
- 16:01:58 [Ralph]
- zakim, this is swd
- 16:01:58 [Zakim]
- ok, Ralph; that matches SW_SWD()11:00AM
- 16:02:05 [Ralph]
- zakim, who's on the call?
- 16:02:05 [Zakim]
- On the phone I see Elisa_Kendall, [LC]
- 16:02:28 [Zakim]
- +Rodrigo
- 16:02:34 [edsu]
- Ralph: you on the phone?
- 16:02:36 [Zakim]
- + +43.123.6aaaa
- 16:02:37 [Zakim]
- +Ralph
- 16:02:43 [berrueta]
- Zakim, Rodrigo is me
- 16:02:43 [Zakim]
- sorry, berrueta, I do not recognize a party named 'Rodrigo'
- 16:02:53 [Clay]
- Clay has joined #swd
- 16:02:54 [Ralph]
- zakim, [lc] is Ed
- 16:02:54 [Zakim]
- +Ed; got it
- 16:02:56 [cgi-irc]
- cgi-irc has joined #swd
- 16:03:01 [Zakim]
- +Antoine_Isaac
- 16:03:10 [Ralph]
- Meeting: SemWeb Deployment WG
- 16:03:17 [JonP]
- JonP has joined #swd
- 16:03:21 [Ralph]
- zakim, aaaa is Guus
- 16:03:21 [Zakim]
- +Guus; got it
- 16:03:22 [berrueta]
- Zakim, Rodrigo is me
- 16:03:22 [Zakim]
- sorry, berrueta, I do not recognize a party named 'Rodrigo'
- 16:03:24 [Zakim]
- +[LC]
- 16:03:28 [aliman]
- aliman has joined #swd
- 16:03:28 [Clay]
- zakim, LC is Clay
- 16:03:28 [Zakim]
- +Clay; got it
- 16:03:35 [Zakim]
- +??P25
- 16:03:55 [Ralph]
- zakim, ??p25 is Alistair
- 16:03:55 [Zakim]
- +Alistair; got it
- 16:03:56 [Zakim]
- + +012242aabb
- 16:04:10 [Ralph]
- zakim, aabb is Quentin
- 16:04:10 [Zakim]
- +Quentin; got it
- 16:04:23 [Ralph]
- zakim, ctic is Diego
- 16:04:23 [Zakim]
- +Diego; got it
- 16:04:43 [Zakim]
- -Guus
- 16:04:54 [Zakim]
- +Jon_Phipps
- 16:04:58 [Ralph]
- Agenda: http://lists.w3.org/Archives/Public/public-swd-wg/2007Dec/0003.html
- 16:05:13 [Ralph]
- -> http://www.w3.org/2007/11/27-swd-minutes.html previous 2007-11-27
- 16:05:37 [JonP]
- zakim, Jon_Phipps is me
- 16:05:37 [Zakim]
- +JonP; got it
- 16:05:39 [Ralph]
- Chair: Guus
- 16:05:48 [Ralph]
- Scribe: Elisa
- 16:06:03 [Ralph]
- scribenick: Elisa
- 16:06:03 [Zakim]
- +??P31
- 16:06:10 [benadida]
- benadida has joined #swd
- 16:06:16 [Ralph]
- zakim, ??p31 is Daniel
- 16:06:16 [Zakim]
- +Daniel; got it
- 16:06:19 [dlrubin]
- dlrubin has joined #swd
- 16:06:32 [Zakim]
- + +1.617.395.aacc
- 16:06:38 [benadida]
- zakim, I am aacc
- 16:06:40 [Zakim]
- +benadida; got it
- 16:06:46 [Zakim]
- +Guus
- 16:07:18 [Ralph]
- zakim, who's on the phone?
- 16:07:18 [Zakim]
- On the phone I see Elisa_Kendall, Ed, Diego, Ralph, Antoine_Isaac, Clay, Alistair, Quentin, JonP, Daniel, benadida, +43.123.6aadd
- 16:07:24 [Simone]
- Zakim, passcode?
- 16:07:24 [Zakim]
- the conference code is 79394 (tel:+1.617.761.6200 tel:+33.4.89.06.34.99 tel:+44.117.370.6152), Simone
- 16:08:07 [Ralph]
- zakim, aadd is probably Simone
- 16:08:07 [Zakim]
- +Simone?; got it
- 16:08:46 [Ralph]
- zakim, Simone is really Guus
- 16:08:46 [Zakim]
- +Guus; got it
- 16:08:52 [Elisa]
- agenda+ Admin
- 16:09:27 [Ralph]
- Regrets: Vit, Justin, Sean
- 16:09:48 [Zakim]
- +??P36
- 16:09:55 [Simone]
- Zakim, ??P36 is me
- 16:09:55 [Zakim]
- +Simone; got it
- 16:10:09 [Elisa]
- PROPOSED: Accept minutes of the November 27th telecon (http://www.w3.org/2007/11/27-swd-minutes.html)
- 16:10:25 [TomB]
- TomB has joined #swd
- 16:10:42 [Elisa]
- RESOLVED: Minutes accepted
- 16:10:43 [Ralph]
- zakim, mute simone
- 16:10:43 [Zakim]
- Simone should now be muted
- 16:11:00 [Elisa]
- Next telecon: 4 December 1600 UTC
- 16:11:04 [Elisa]
- agenda+ SKOS
- 16:11:14 [Zakim]
- +??P38
- 16:11:26 [TomB]
- zakim, ??P38 is TomB
- 16:11:26 [Zakim]
- +TomB; got it
- 16:12:36 [Elisa]
- Review of Editor's draft - continued
- 16:12:44 [Elisa]
- Review of primer - continued
- 16:12:49 [Elisa]
- Issue 39 discussion
- 16:12:57 [Antoine]
- http://www.w3.org/2006/07/SWD/wiki/SkosDesign/ConceptualMapping/ProposalTwo
- 16:13:47 [Elisa]
- issue of mapping links, using existing relationships in SKOS to create mapping links was original approach
- 16:14:20 [Elisa]
- this new proposal is much more conservative
- 16:14:56 [Elisa]
- takes text from existing mapping vocabulary, and introduces two new concepts: related match and overlapping match
- 16:15:13 [Elisa]
- deprecates major and minor match elements from current mapping vocabulary
- 16:15:37 [Elisa]
- proposal is to delegate status of these elements to "concept coordination"
- 16:16:03 [Ralph]
- rrsagent, please make record public
- 16:16:39 [Elisa]
- SKOS mapping coordination constructs: and, or, not
- 16:16:59 [Elisa]
- the proposal attempts to establish some formal semantics for these constructs
- 16:17:16 [Elisa]
- including domain, range
- 16:17:38 [Elisa]
- semantics are to be discussed, e.g., exact match is transitive
- 16:18:27 [Elisa]
- section 3 covers other issues, includes example of animal ontologies, attempts to match them
- 16:18:52 [Elisa]
- concludes with relation rules, intended semantics, issues leading to decisions in the proposal
- 16:19:10 [Guus]
- q+
- 16:19:12 [Elisa]
- for example replacing major, minor match with overlapping match
- 16:19:46 [Elisa]
- raises issue on building mapping links between collections that are not SKOS vocabularies explicitly
- 16:20:17 [Elisa]
- Guus: so, would like to have discussion on a few points in the proposal
- 16:20:35 [Elisa]
- why to we need exact match, and why can't we use OWL same as
- 16:21:00 [Elisa]
- Antoine: the problem is when you use OWL same as, you essentially merge the two schemes
- 16:21:13 [Elisa]
- which the original author may not want to do
- 16:21:34 [Elisa]
- Guus: the point is to have this rationale in the proposal for documentation purposes
- 16:21:57 [Elisa]
- you could also point to why you can't use OWL different class
- 16:22:03 [Elisa]
- both points can be made here
- 16:22:09 [Elisa]
- Antoine: ok
- 16:22:37 [Elisa]
- Guus: is it also possible to summarize the main point of the follow-up email discussion
- 16:23:55 [Elisa]
- Antoine: issues raised - considered that there was a clear distinction between skos mapping relations
- 16:24:44 [Elisa]
- between different concept schemes can still use standard concept relations between concept schemes
- 16:24:50 [Elisa]
- but this would not be for mapping
- 16:25:20 [Elisa]
- Guus: is it inconsistent to use one of the mapping relationships in the same scheme
- 16:25:41 [Elisa]
- Antoine: no
- 16:26:02 [Elisa]
- Guus: this is a borderline case, we should cover how someone might want to use the mapping concepts
- 16:26:20 [Elisa]
- to do this -- the main point would be to make a statement about this
- 16:26:29 [Elisa]
- this should hold for all of the mapping relations
- 16:26:38 [Elisa]
- Antoine: fine
- 16:26:56 [Elisa]
- Guus: what is the typical example of ... I don't really understand the overlapping match
- 16:27:17 [Elisa]
- Antoine: the overlapping match more or less replaces the major and minor match
- 16:27:41 [Elisa]
- this describes relations that are in a mapping - relationships that are common to two mappings
- 16:28:14 [Elisa]
- you have relations with significant semantic load; if concepts are related in this way there are other concepts that a user should
- 16:28:16 [aliman]
- q+ to represent Javier's point about related vs. overlapping
- 16:28:30 [Elisa]
- consider
- 16:29:33 [Elisa]
- it isn't 100% clear where you might use these - Emma McCulloch will provide additional examples
- 16:29:46 [Elisa]
- Guus: do you think there are convincing use cases
- 16:30:01 [Elisa]
- Alistair: I haven't seen use cases
- 16:30:10 [Elisa]
- Guus: this seems rather arbitrary
- 16:30:23 [Zakim]
- -Daniel
- 16:30:39 [Elisa]
- The point came from Javier ... the general point was that the types of inexact or overlapping
- 16:31:00 [Elisa]
- relations you might find are different in nature from associative relationships between thesauri
- 16:31:31 [Elisa]
- so there might be for example overlaps between two thesauri that cover a common time period
- 16:31:52 [Elisa]
- there is no precedent for this in the thesaurus community, and this seems to be
- 16:31:57 [Elisa]
- limited to time and place
- 16:32:18 [aliman]
- q-
- 16:32:28 [Elisa]
- Guus: this seems a rather specific solution, not sufficient evidence to warrant includes
- 16:32:41 [Elisa]
- perhaps we could keep it as a separate option
- 16:32:45 [aliman]
- +1 on guus position regarding "overlapping" property
- 16:33:01 [Elisa]
- if we go for a separate proposal for mapping terminology
- 16:33:24 [Elisa]
- Antoine: we could keep this separate - I can be ok with that
- 16:33:45 [Elisa]
- Guus: do you think, given the comments, this is sufficient to move this forward for next time
- 16:34:03 [Elisa]
- Antoine: yes, but feedback under the specific semantics/axioms would be useful
- 16:34:24 [Elisa]
- if people think there are useful axioms to have there, that would be good feedback
- 16:34:55 [Elisa]
- Guus: so we can leave this action, and move it forward for next week
- 16:35:27 [Elisa]
- -- ISSUE 39 Conceptual mapping links
- 16:35:27 [Elisa]
- http://www.w3.org/2006/07/SWD/track/issues/39
- 16:35:52 [Elisa]
- ACTION: Antoine to come up with a revised proposal based on the comments received
- 16:36:21 [Elisa]
- SKOS Extension Module - no action
- 16:36:30 [Elisa]
- Concept schemes - continued
- 16:36:41 [Antoine]
- q+ on SKOS-XL
- 16:36:53 [Elisa]
- no progress on isDefinedBy (continued)
- 16:37:06 [Elisa]
- Statement on issue 44 from Alistair ...
- 16:37:47 [Elisa]
- Alistair: Antoine raises concern about what might happen if we say nothing about the transitivity of SKOS broader
- 16:38:16 [Elisa]
- if we allow people to make either choice, people will make conflicting decisions, which is a valid concern
- 16:39:28 [Elisa]
- he proposes the notion of a locally transitive relationship, also see Alan Rector's comment in the SWBP note in simple part whole
- 16:39:45 [Elisa]
- this is a serious concern that needs to be addressed
- 16:40:05 [Elisa]
- Guus: ok with respect to producing a reference, when can we expect something?
- 16:40:17 [TomB]
- [http://www.w3.org/2001/sw/BestPractices/OEP/SimplePartWhole/ Simple part-whole relations in OWL Ontologies]
- 16:40:22 [Elisa]
- Alistair: it depends on how far we want to get before putting out a first draft
- 16:40:52 [Elisa]
- if we want something to be reviewed before Christmas, publishing something as an editor's draft before Christmas
- 16:41:15 [Elisa]
- Guus: assuming that Antoine moves his proposal forward, it doesn't seem far fetched
- 16:41:40 [Elisa]
- Alistair: we could, and then throw stones at it ... it certainly needs to go in there
- 16:42:00 [Elisa]
- Guus: that would mean that we produce a new draft before Christmas, and use the Christmas period for review
- 16:42:10 [Elisa]
- Alistair: work on what we've got more or less right now
- 16:42:22 [Elisa]
- Guus: yes, and go forward with that
- 16:42:49 [Elisa]
- Alistair: we talked about a rules of thumb appendix, to show examples of how to do something sensible,
- 16:42:56 [Elisa]
- requires some of Sean's time, who is traveling
- 16:43:03 [Elisa]
- agenda+ RDFa
- 16:43:50 [Elisa]
- Ben: the central issue is related on exactly how we do chaining and how we deal with instance of
- 16:43:56 [aliman]
- q+ what's chaining?
- 16:44:09 [Elisa]
- we have agreement in the group that this is the last major issue to deal with
- 16:44:24 [Elisa]
- assuming we don't hit any snags, and fix the use cases for the new proposal on chaining
- 16:44:37 [Guus]
- zakim, who is here?
- 16:44:37 [Zakim]
- On the phone I see Elisa_Kendall, Ed, Diego, Ralph, Antoine_Isaac, Clay, Alistair, Quentin, JonP, benadida, Guus, Simone (muted), TomB (muted)
- 16:44:39 [Zakim]
- On IRC I see TomB, dlrubin, benadida, aliman, JonP, cgi-irc, Clay, edsu, Simone, Zakim, RRSAgent, Ralph, Antoine, berrueta, Elisa, Guus
- 16:44:55 [Elisa]
- I've update the schedule, we're pushing hard to get the syntax with this new proposal in over the next 10 days
- 16:45:17 [Elisa]
- it would be good to get people on the call to review the new syntax before Christmas
- 16:45:27 [Elisa]
- Guus: didn't we have reviewers for the first working draft
- 16:45:48 [Elisa]
- Ben: yes, we're just tweaking it for the latest changes, hoping this will go to last call
- 16:46:23 [Elisa]
- Guus: we should use the same reviewers
- 16:46:30 [Elisa]
- Antoine did the primer
- 16:46:39 [Elisa]
- Diego: I did a review, the other one was Ed
- 16:46:59 [Elisa]
- Ben: are you willing to review again, and if so, what would the schedule be
- 16:47:04 [Elisa]
- Diego: yes
- 16:47:12 [Elisa]
- Ed: yes I'd be willing to do this again
- 16:47:37 [Elisa]
- Ben: in two weeks -- would you still have time to review this before the holidays
- 16:47:50 [Elisa]
- Ed: yes if it hasn't changed substantially
- 16:48:02 [Elisa]
- Ben: there is one notable change which we will explain
- 16:48:09 [Elisa]
- Ed: yes this would be fine
- 16:48:15 [Elisa]
- Diego: yes, ok
- 16:48:34 [Elisa]
- Guus: will this be a working draft
- 16:49:01 [Elisa]
- Ben: this would be a working draft leading to last call ... how does this work? you publish a working draft and then say it is going to last call?
- 16:49:16 [Elisa]
- Guus: we agreed that the decision for last call would be taken by both groups
- 16:49:25 [Elisa]
- we could make a decision on the first call in January
- 16:49:46 [Elisa]
- we should check with Stephen if they can take a decision by the first call in Januar
- 16:50:33 [Elisa]
- you need to send a proposal to the WG to promote the doc to last call (to both groups, pointing to responses to comments ...document precisely what has happened with the comments)
- 16:50:50 [Elisa]
- then you have to set a last call period
- 16:51:02 [Elisa]
- normally the comment period is between 4 and 6 weeks
- 16:51:15 [Elisa]
- Ben: the commenting period starts after the WG is published, correct?
- 16:52:07 [Elisa]
- it would be good to prepare a list that you want to send the last call to, also potentially track comments
- 16:52:15 [Elisa]
- issue tracker would be fine
- 16:52:36 [Elisa]
- Ralph -- what would your proposal be for tracking comments?
- 16:52:48 [Elisa]
- Ralph: absolutely, the issue tracker
- 16:53:07 [Elisa]
- Ben: ok, you'll most likely hear from me as I work through the process
- 16:53:17 [Elisa]
- Guus: are there any potential sources of delay?
- 16:53:47 [Elisa]
- Ben: the one potential issue is the one we're working on ... if we find things in the test process, then there are possibilities there
- 16:54:02 [Elisa]
- we have 4-5 implementations that will signal an issue quickly at this point
- 16:54:22 [Elisa]
- Guus: then you should prepare an implementation report during the last call period
- 16:54:34 [Elisa]
- Ben: we are definitely prepared to do so
- 16:54:45 [Elisa]
- Guus: agenda+ Recipes
- 16:55:00 [Elisa]
- agenda+ Recipies
- 16:55:17 [Ralph]
- -> http://lists.w3.org/Archives/Public/public-swd-wg/2007Dec/0006.html Revised Recipes posted [Jon 3-Dec]
- 16:55:19 [Elisa]
- Guus: I think I saw progress on the recipies as well
- 16:55:46 [dlrubin]
- dlrubin has left #swd
- 16:55:53 [Ralph]
- Topic: Recipes
- 16:56:02 [Elisa]
- Jon: we've put up a new editor's draft - I think it covers all of the issues except that it's broken under certain circumstances
- 16:56:18 [Ralph]
- -> http://www.w3.org/2006/07/SWD/recipes/draft-20071203 Recipes Editor's Draft of 2007-12-03
- 16:56:41 [Elisa]
- which has to do with Apache redirect (1st action under recipes, which is continued)
- 16:56:54 [Elisa]
- Ralph: I think my action still needs to be addressed ...
- 16:57:17 [Elisa]
- Jon: I think we've dealt with that but of course we have a new one for you, which is action 24, the next one
- 16:57:49 [Elisa]
- ACTION: Dan to ask apache about conditional redirects [recorded in [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action18] CONTINUES
- 16:58:00 [Ralph]
- -> http://www.w3.org/2006/07/SWD/track/products/5 Open Issues on Recipes
- 16:58:01 [Elisa]
- ACTION: Diego to recast Recipe 6 [recorded in [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action19]
- 16:58:09 [Elisa]
- COMPLETED
- 16:58:21 [Elisa]
- ACTION: Jon to add words that acknowledge the existence of RDFa as [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action21]
- 16:58:28 [Elisa]
- COMPLETED
- 16:59:29 [Elisa]
- DROPPED ACTION: Jon to make changes as proposed [with regard to Issue-23] [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action22]
- 17:00:30 [Elisa]
- ACTION 23 is being Dropped
- 17:00:39 [Elisa]
- Action 24 continues
- 17:00:55 [Ralph]
- s/DROPPED ACTION: Jon/DONE ACTION: Jon/
- 17:00:58 [Elisa]
- Action 25 continues
- 17:01:23 [Elisa]
- COMPLETED ACTION: TF leaders to prepare a version of Recipes for review in [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action26]
- 17:01:38 [Elisa]
- COMPLETEDACTION: diego to update deliverables page w/r/t recipes document [recorded in http://www.w3.org/2007/11/27-swd-minutes.html#action20]
- 17:02:16 [Elisa]
- Guus: still need to solicit reviews for this -- when would reviewers be needed
- 17:02:45 [Elisa]
- Jon: any time, I guess -- we're just missing that one piece, which I guess is fairly critical
- 17:03:02 [Elisa]
- Guus: we should solicit reviews at this point, though
- 17:03:18 [Elisa]
- Ralph: I'll certainly review it
- 17:04:36 [Elisa]
- Guus: adjourn
- 17:04:39 [Zakim]
- -Quentin
- 17:04:41 [Zakim]
- -Alistair
- 17:04:43 [Zakim]
- -Ed
- 17:04:44 [Zakim]
- -Ralph
- 17:04:46 [Zakim]
- -JonP
- 17:04:50 [Zakim]
- -Diego
- 17:04:52 [Zakim]
- -Guus
- 17:04:56 [Zakim]
- -benadida
- 17:04:58 [Zakim]
- -Clay
- 17:05:00 [Zakim]
- -TomB
- 17:05:02 [edsu]
- Antoine: were we going to chat about primer?
- 17:05:04 [Zakim]
- -Simone
- 17:05:37 [Ralph]
- zakim, list participants
- 17:05:37 [Zakim]
- As of this point the attendees have been Elisa_Kendall, Rodrigo, +43.123.6aaaa, Ralph, Ed, Antoine_Isaac, Guus, Clay, Alistair, +012242aabb, Quentin, Diego, JonP, Daniel,
- 17:05:41 [Zakim]
- ... +1.617.395.aacc, benadida, Simone?, Simone, TomB
- 17:05:50 [Ralph]
- rrsagent, please draft minutes
- 17:05:50 [RRSAgent]
- I have made the request to generate http://www.w3.org/2007/12/04-swd-minutes.html Ralph
- 17:06:20 [edsu]
- i'll call back, one sec
- 17:07:24 [edsu]
- rats it says "conference restricted at this time"
- 17:07:42 [edsu]
- i can call you direct
- 17:08:14 [edsu]
- what number are you at?
- 17:08:17 [edsu]
- got it
- 17:09:54 [edsu]
- seeya
- 17:10:21 [Zakim]
- -Antoine_Isaac
- 17:11:07 [edsu]
- edsu has left #swd
- 17:11:40 [Antoine]
- Antoine has left #swd
- 17:15:21 [Zakim]
- disconnecting the lone participant, Elisa_Kendall, in SW_SWD()11:00AM
- 17:15:25 [Zakim]
- -Elisa_Kendall
- 17:15:50 [Zakim]
- SW_SWD()11:00AM has ended
- 17:15:52 [Zakim]
- Attendees were Elisa_Kendall, Rodrigo, +43.123.6aaaa, Ralph, Ed, Antoine_Isaac, Guus, Clay, Alistair, +012242aabb, Quentin, Diego, JonP, Daniel, +1.617.395.aacc, benadida, Simone?,
- 17:15:54 [Zakim]
- ... Simone, TomB
- 17:16:35 [Elisa]
- ok -- will do, thanks
- 17:17:06 [Ralph]
- zakim, bye\
- 17:17:06 [Zakim]
- I don't understand 'bye\', Ralph
- 17:17:12 [Ralph]
- rrsagent, bye
- 17:17:12 [RRSAgent]
- I see 4 open action items saved in http://www.w3.org/2007/12/04-swd-actions.rdf :
- 17:17:12 [RRSAgent]
- ACTION: Antoine to come up with a revised proposal based on the comments received [1]
- 17:17:12 [RRSAgent]
- recorded in http://www.w3.org/2007/12/04-swd-irc#T16-35-52
- 17:17:12 [RRSAgent]
- ACTION: Dan to ask apache about conditional redirects [recorded in [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action18] CONTINUES [2]
- 17:17:12 [RRSAgent]
- recorded in http://www.w3.org/2007/12/04-swd-irc#T16-57-49
- 17:17:12 [RRSAgent]
- ACTION: Diego to recast Recipe 6 [recorded in [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action19] [3]
- 17:17:12 [RRSAgent]
- recorded in http://www.w3.org/2007/12/04-swd-irc#T16-58-01
- 17:17:12 [RRSAgent]
- ACTION: Jon to add words that acknowledge the existence of RDFa as [recorded in http://www.w3.org/2007/11/20-swd-minutes.html#action21] [4]
- 17:17:12 [RRSAgent]
- recorded in http://www.w3.org/2007/12/04-swd-irc#T16-58-21