Re: [MMUSIC] Trafficclass Attribute -02 submitted
"Paul E. Jones" <paulej@packetizer.com> Thu, 23 August 2012 20:28 UTC
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From: "Paul E. Jones" <paulej@packetizer.com>
To: 'Paul Kyzivat' <pkyzivat@alum.mit.edu>
References: <201207171919.q6HJJQij014492@mtv-core-3.cisco.com> <5005DBCA.8040405@alum.mit.edu> <002f01cd80b2$24455530$6ccfff90$@packetizer.com> <50356E1D.4030908@alum.mit.edu>
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Date: Thu, 23 Aug 2012 16:29:00 -0400
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Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] Trafficclass Attribute -02 submitted
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Paul, > > We want to allow a leading underscore. So, perhaps this: > > tcl-token = (ALPHA / "_") 0*(ALPHA / DIGIT) 0*(("-" / "_") 1*(ALPHA > > / > > DIGIT)) > > Well, there are two things to deal with: > - what forms are allowed > - how to represent that in ABNF > > Well formed ABNF can answer both questions, as long as it isn't so obscure > that people don't understand it. > > I'm not in love with the leading "_" to signal non-standard adjectives, > but neither do I hate it. But I'm much less fond of sequences of _ and -. This is understandable, and it's also the subject of RFC 6648. While I might get shot for saying so, I actually do prefer having some means of indicating that a value is non-standard. At least then people can know to ignore it. My personal opinion is that allowing "_foo" means that people are creating their own risk. That's fine. Disallowing "_foo" means people will use "foo" and then one day when the IETF standardizing "foo" we have two values with perhaps very different meanings. > Do you want "foo:_bar" to be a valid adjective? How about "_foo:bar"? An "adjective" is the who string in each example, so both should be legal. > ISTM that foo:_bar is probably a bad idea. So I'm thinking it would be > better to define tcl_token so it doesn't permit a leading underscore. > Then define the adjectives to allow the leading underscore where you want > it. The reason I want to allow "foo:_bar" is for the same reasons we allow "_foo" or other vendor-specific value. If we define a class of adjectives (e.g, "aq:" or "pri:"), some vendor might have a value that fits within that class. So, they use "aq:_foo". I don't think it's a bad idea at all. As I mentioned before, the adjective is the whole string, so it is either known or not as a unit. If someone cares to see that this is an adjective in a known class, they can match on "aq:". The "_foo" part is just treated as an unknown value. > So perhaps: > > tcl-sep = "-" / "_" > > tcl_token = ALPHA 0*(ALPHA / DIGIT) 0*((tcl-sep 1*(ALPHA / DIGIT)) > > std-unclassified-adj = tcl-token > > std-adj-classifier = std-unclassified-adj ":" > > adj-qualifier = tcl-token > > std-classified_adj = std-adj-classifier adj-qualifier > > standard-adjective = std-unclassified-adj / std-classified-adj > > non-standard-adjective = "_" standard-adjective Introducing "tcl-sep" might be reasonable, but I think we're making this unnecessarily complex introducing "std-adj..." and "non-standard-adj..." productions. What benefit do we get from that? I would prefer the "_" (when it is leading) to be understood as non-standard, but I don't really want to create parallel syntax. > >> Also, your syntax doesn't cover non-standard-adjectives. You could > >> cover that by: > >> > >> adjective = standard-adjective / non-standard-adjective > >> > >> standard-adjective = classified-adjective / > >> unclassified-adjective > >> > >> non-standard-adjective = "_" standard-adjective > > > > I don't think we should separate standard and non-standard adjectives > > via syntax. If we have a particular interpretation of "_foo" to mean > > that it is non-standard, I think the above syntax will work. We just > > need to explain that adjectives with leading underscores are for non- > standard use. > > Hopefully I made a case above for putting it into the syntax. If we really want to separate out standard and non-standard adjectives with separate syntax, yes, I think you accomplished that (modulo the fact one cannot have "aq:_foo"). > >> IIUC, 'aq', 'admitted', 'non-admitted', and 'none' are *not* > >> Unqualified adjectives. Rather, > >> > >> 'aq:admitted', 'aq:non-admitted', and 'aq:none' are *qualified* > >> adjectives. > >> > >> Does the distinction matter for registration? Should there be > >> different criteria for registering new qualified adjectives? Maybe > >> so. Maybe there should be some review of whether the new 'aq:foo' is > >> compatible with the intended meaning of 'aq'??? > > > > "aq" by itself is not an adjective. "aq:admitted" is an adjective. > > I see nothing to prevent both "aq" and "aq:admitted" from being > registered. If you don't want to permit that, then say so. We could do that, but is there benefit in doing so? It would potentially mean a 4-level registration (category, application, adjective-prefix, adjective suffix). I really have no idea what people would prefer there. I have no preference. I just don't want to make it complicated. > > What I would like to do is have a multi-level registration akin to > > what we have for media types. So, we would have something like this: > > > > +----------------------+----------------------+----------------------+ > > | Category | Application | Adjective | > > +----------------------+----------------------+----------------------+ > > | conversational | audio | immersive | \ ... / > > The structure of the registry can be settled later. Work out the desired > usage first. (But to get all that into IANA will be difficult.) > > My first thought is that IANA can simply register standard-adjectives > without regard for whether they are qualified or not. The ones that are > qualified will sort together. That's what I was hoping to do by just having three levels. I displayed the "aq:" separately, but what I would expect to see on the web page would be just the sorted list, as you said. > But you might want a higher bar for registering a new adj-qualifier for an > existing std-adj-classifier than you do for registering a new std- > unclassified-adj. That will require more complex rules, and *might* > require a different table structure. > > E.g. > > suppose aq:admitted and aq:non-admitted have already been registered. > > Would you want it to be ok to register aq:foo for some purpose unrelated > to the other two? I think not. What guidelines would you want to give to > an expert to ensure that doesn't happen? Yeah, agreed. > (If there are no guidelines, and someone attempts to do this, the expert > has no grounds other than his own opinion to reject the request.) Understood. Paul
- [MMUSIC] Trafficclass Attribute -02 submitted James Polk
- Re: [MMUSIC] Trafficclass Attribute -02 submitted Paul Kyzivat
- Re: [MMUSIC] Trafficclass Attribute -02 submitted Paul Kyzivat
- Re: [MMUSIC] Trafficclass Attribute -02 submitted Paul E. Jones
- Re: [MMUSIC] Trafficclass Attribute -02 submitted Paul Kyzivat
- Re: [MMUSIC] Trafficclass Attribute -02 submitted Paul E. Jones