Re: [Ietf-message-headers] provisional registration Memento-Datetime header

Herbert van de Sompel <hvdsomp@gmail.com> Wed, 29 September 2010 19:33 UTC

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Date: Wed, 29 Sep 2010 13:33:52 -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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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.



> 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<http://www.ietf.org/rfc/rfc2616.txt> "Hypertext
Transfer Protocol -- HTTP/1.1".



> 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;
(*) 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.

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.)

As indicated, this is definitely an area that requires further discussion.
Thanks for bringing it up.



> 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/