Re: [Ietf-message-headers] provisional registration Memento-Datetime header
Herbert van de Sompel <hvdsomp@gmail.com> Wed, 29 September 2010 21:15 UTC
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Date: Wed, 29 Sep 2010 15:16:23 -0600
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From: Herbert van de Sompel <hvdsomp@gmail.com>
To: Ted Hardie <ted.ietf@gmail.com>
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Cc: "Michael L. Nelson" <mln@cs.odu.edu>, Ietf-message-headers@ietf.org
Subject: Re: [Ietf-message-headers] provisional registration Memento-Datetime header
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Thanks a lot for your input, Ted. We will definitely include the BNF in our Internet Draft. I am afraid we will not be able to make it to Bejing. Several of us work at a US government lab and traveling to China is not considered ... err ... essential for us. But we will definitely try and attend the meeting after Bejing, and look forward to a discussion of the Memento Internet Draft, there. And, obviously, issues can already be discussed on memento-dev@googlegroups.com. Greetings Herbert On Wed, Sep 29, 2010 at 3:07 PM, Ted Hardie <ted.ietf@gmail.com> wrote: > Some comments in-line. > > On Wed, Sep 29, 2010 at 12:33 PM, Herbert van de Sompel > <hvdsomp@gmail.com> wrote: > > Dear Ted, > > Thanks for your feedback. I insert a few comments, below. > > Cheers > > Herbert > > > > On Wed, Sep 29, 2010 at 12:14 PM, Ted Hardie <ted.ietf@gmail.com> wrote: > >> > >> Howdy, > >> > >> First, I would suggest that the pointer given in the specification > >> document > >> be to the introduction document > >> (http://www.mementoweb.org/guide/quick-intro/) > >> because leaping into the middle of the guide cited doesn't tell you > >> anything > >> about what this is for. Without that, it is sort of hard to tell > >> whether the header > >> is well-specified. > >> > > > > Will do when we submit the request for registration in the temporal > > registry, in a few weeks from now. However, at that point we may have a > > first version of the Memento Internet Draft available, which would then > be a > > better point of reference. > > > > An Internet-draft this would be great; thanks for following through with > this. > > >> > >> Second, I would suggest that you include in the linked document ( > >> guide or other) > >> ABNF or similar pseudo-code indicating what you expect in the two > >> headers you are > >> dealing with. This would tell a develop whether or not q-factors are > >> permitted, > >> for example. > >> > > > > The possible values for Memento-Datetime (and its associated > Accept-Datetime > > request header) are specified as: > > In the below transactions, values for the Accept-Datetime and > > Memento-Datetime headers are datetimes expressed according to the RFC > 1123 > > format referenced in Section 3.3.1 of RFC 2616 "Hypertext Transfer > Protocol > > -- HTTP/1.1". > > > > So, I find that a somewhat convoluted way of expressing this. As you > no doubt recognize, > RFC 2616 discusses three different date formats, and RFC 1123 is a > fairly bare-bones > update to RFC 822, with not a lot of discussion of why the change is > there. Rather > than have folks follow the links and potentially get confused, why not > include it? The production > in RFC 2616 is fairly easy to provide: > > rfc1123-date = wkday "," SP date1 SP time SP "GMT" > date1 = 2DIGIT SP month SP 4DIGIT > ; day month year (e.g., 02 Jun 1982) > time = 2DIGIT ":" 2DIGIT ":" 2DIGIT > ; 00:00:00 - 23:59:59 > weekday = "Monday" | "Tuesday" | "Wednesday" > | "Thursday" | "Friday" | "Saturday" | "Sunday" > month = "Jan" | "Feb" | "Mar" | "Apr" > | "May" | "Jun" | "Jul" | "Aug" > | "Sep" | "Oct" | "Nov" | "Dec" > > I would personally err on the side of including it, along with > a reference to the source. This is largely a stylistic matter, of course, > as long as other readers are clear on what to produce and parse. > > >> > >> Third, I would suggest you consider a modification similar to that in > >> Accept-Language, > >> allowing you to include a series of time values and q factors for > >> them. If you would really > >> like August 28, 1963, but would okay with August 29, 1963 or August > >> 30, 1963, the > >> q-factors would allow you indicate which would be better. I also > >> strongly suspect > >> that if you don't do this some bright spark will do it for you later, > >> as we've seen > >> q-factor additions crop up to Accept headers in a variety of > "Interesting" > >> ways. > >> > > > > This is something that definitely needs further exploration and > discussion. > > The first version of the Memento Internet Draft will most likely not > address > > this, but it has come up in our discussions several times. To cut a long > > story short, we are not sure that the q-value approach would add > significant > > value to datetime negotiation, mainly because: > > (*) The variant resources exist on a (time) continuum, and are not > discreet > > as with other dimensions of HTTP content negotiation; > > Not to be pedantic, but the resources are discreet. Each resource endures > for a specific period, which may or may not be known. > > > (*) In an archival context, one should be very happy to actually find an > > archival resource in the neighborhood of a specified datetime; expressing > > multiple preferences with associated q-values feels a bit disconnected > from > > this reality. > > But once you have create the header, you need to understand that it may be > used in multiple ways. As an example, what happens when someone wants > to use this > using future dates, as part of a pub/sub mechanism? > > > As an alternative approach that might be more aligned with datetime > > negotiation (in a continuum), we have been thinking about the ability to > > express a duration interval around a datetime mid-point, e.g.: > > Accept-Datetime: Tue, 11 Sep 2001 20:35:00 GMT; P10D > > would be used to request archival resources in an interval of +/- 10 days > > around Tue, 11 Sep 2001 20:35:00 GMT (the xsd:duration syntax is used to > > express the interval, but that is just to convey the idea not to propose > an > > actual syntax.) > > In an HTTP context, if there are 5 resources within the duration > interval what is returned > and how are they ordered? If you have a q-value, you can identify > which one should > be returned. Alternatively, you can return all of them in a multipart > with appropriate metadata; > for some resources this is practical, but it may not be so for all. > > > > As indicated, this is definitely an area that requires further > discussion. > > Thanks for bringing it up. > > Any chance one of the authors will be at the Beijing IETF? I think > this discussion > would be a useful one to have at the APPs area meeting new APPSWG meeting. > You might also consider posting it to apps-open for discussion, when you > are > ready to discuss the duration issue. > > regards, > > Ted Hardie > > > > >> > >> regards, > >> > >> Ted Hardie > >> > >> On Wed, Sep 29, 2010 at 10:18 AM, Herbert Van de Sompel > >> <hvdsomp@gmail.com> wrote: > >> > PROVISIONAL MESSAGE HEADER FIELD SUBMISSION TEMPLATE: > >> > Header field name: Memento-Datetime > >> > Applicable protocol: http > >> > Status: provisional > >> > Author/Change controller: Herbert Van de Sompel, hvdsomp@gmail.com > , > >> > Los > >> > Alamos National Laboratory, http://public.lanl.gov/herbertv/ > >> > Specification document(s): http://www.mementoweb.org/guide/http/ > >> > Related information: > >> > > >> > Van de Sompel, H., Sanderson, R., Nelson, M.L., Balakireva, L., > >> > Ainsworth, > >> > S., Shankar, H. (2010) An HTTP-Based Versioning Mechanism for Linked > >> > Data. > >> > Proceedings of the 3rd Workshop on Linked Data on the Web > >> > (LDOW2010).Arxiv > >> > preprint. http://arxiv.org/abs/1003.3661 > >> > > >> > Van de Sompel, H., Nelson, M.L., Sanderson, R., Balakireva, L., > >> > Ainsworth, > >> > S., Shankar, H. (2009) Memento: Time Travel for the Web. Arxiv > preprint. > >> > http://arxiv.org/abs/0911.1112 > >> > > >> > > >> > _______________________________________________ > >> > Ietf-message-headers mailing list > >> > Ietf-message-headers@ietf.org > >> > https://www.ietf.org/mailman/listinfo/ietf-message-headers > >> > > >> > > > > > > > > > -- > > Herbert Van de Sompel > > Digital Library Research & Prototyping > > Los Alamos National Laboratory, Research Library > > http://public.lanl.gov/herbertv/ > > > -- Herbert Van de Sompel Digital Library Research & Prototyping Los Alamos National Laboratory, Research Library http://public.lanl.gov/herbertv/
- [Ietf-message-headers] provisional registration M… Herbert Van de Sompel
- Re: [Ietf-message-headers] provisional registrati… Ted Hardie
- Re: [Ietf-message-headers] provisional registrati… Herbert van de Sompel
- Re: [Ietf-message-headers] provisional registrati… Ted Hardie
- Re: [Ietf-message-headers] provisional registrati… Herbert van de Sompel
- Re: [Ietf-message-headers] provisional registrati… SM
- Re: [Ietf-message-headers] provisional registrati… Herbert Van de Sompel