Subject: Re: [urn] Suggested PWID URN for Persistent Web IDentifiers - version 3

From: [email-masked] (Dale R. Worley)
Date: Sat, 08 Sep 2018 10:08:37 -0400

Re-reading this thread, I think Henry's comments are significant in
regard to how this proposal will interact with actual archive use.  I
don't know enough about archiving to speak well to that, but there are
significant technical points that seem to be connect with or parallel
Henry's archiving considerations.

One critical element is the archive identifier.  There seem to be two
cases regarding what is intended.

One case is where the PWID URNs are constructed by archive organization
itself.  Thus, the archive organization can choose the archive
identifier, and presumably that will be a domain name that it controls.
That is not a perfect solution (we've had trouble with it in other URN
proposals), but it's clear.  But in that situation, the archive is
probably already minting URLs that can be used to retrieve archived
resources, so it's not clear that there is a large benefit to be gained.

The other case is where the URNs are constructed by third parties, that
is, neither the archive nor the consumer of the URN.  As Henry says,
this usage has the nature of a citation.  What is unclear in this case
is who selects the archive identifier of the archive.

One possibility in this case is that it is expected that there will be
only a small number of archives, and there's an IANA registry of archive
identifiers, and any person is allowed to register an identifier for any
archive.  Presumably, expert review could be used to keep the situation
under control.  This is alluded to by:

      On long term, there should be created a registry that keeps track
      of identifiers of archives over time, since they are likely to
      change names, merge etc. when taking about a 100 year period.

The proposal generally assumes that an archived resource can be
identified using just:
- the archive identifier
- the URL whose contents were archived
- the time at which the contents were archived

Embedding the URL into the URN presents syntactic problems.  The
characters [ and ] can be used in the host-address part of a URL, and ?
is used for queries.  The latter I consider to be particularly
important, as web links can often include query-parts.  This problem
needs to be solved, as a syntax that "covers about 80-95% of all cases"
is a syntax that doesn't suffice for the problem at hand.

I don't see a need to worry about fragment-parts of archived URLs, as
the fragment structure is inherently embedded in the resource retrieved
via the URL.  So an archive can archive the URL-without-fragment, the
URN can reference that URL, and user can attach the required
fragment-part to the URN to specify the desired fragment.

There is some lack of clarity about coverage-spec.  If the "coverage" is
*part* of the archived resource, then it is, or should be, a fragment,
and that can be specified by appending a fragment-part to the URN.  If
the coverage is metadata about the resource, it seems to be undefined
what forms the metadata resource could take.  But some coverage values
seem to suggest that the referenced information is a set of resources
which contains as a member the resource designated by the recorded URL.
This concept gets very interesting indeed.  There doesn't seem to be any
defined resource type for "a web site", or even "all the files needed to
display a web page".  Also, it's not clear what the archival-time means
in this context, since presumably the archive need not contain archived
copies of everything in the aggregate that were all made at the
specified archival-time.

Dale

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From: [email-masked] (Dale R. Worley)
Date: Sat, 08 Sep 2018 22:27:00 -0400

Thinking again about PWIDs as citations ...

One feature of a citation is that it's not just an identifier for
retrieving a specific instance of a resource.  If that instance is
unavailable, information can be extracted from the citation that can be
used to retrieve other instances of the resource.  I.e., if the cited
instance is in Library A, information from the citation (author, title,
etc.) can be used to locate another instance in Library B.  The citation
is *transparent* as a source of information for *partial matching*
against the universe of information resources.

>From this point of view, retrieval URLs for web archives are *opaque*,
at least, unless one knows the specifics of how each archive constructs
its URLs.

But PWID URNs are *transparent*; the archived URL and timestamp can be
extracted from the URN algorithmicly.  And those can be used to search
other web archives for similar archived resources.  (Presumably, other
archives don't have archived resources with exactly the same
timestamps.)

Conversely, if the archives are amenable, we can have straightforward
resolution by having each archive register a URL prefix with IANA.  Like
the current DOI resolver, when a URN is prefixed with its archive's URL
prefix and then fetched, the referenced resource is returned.

And I think this combination of features is something new -- PWIDs could
be *algorithmicly resolvable* (using their specified archives), and yet
also be *citations* (transparently providing enough information that a
human can find similar resources in other archives).

Dale

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From: Eld Zierau <[email-masked]>
Date: Mon, 10 Sep 2018 13:44:03 +0000

Please be aware that I will answer this later - but due to a very busy period (workwise, in connection with the iPRES conference and having one weeks holiday) I may not be able to get time to answer before after iPRES - that means in start of October
Best regards, Eld

-----Original Message-----
From: Dale R. Worley <[email-masked]> 
Sent: Sunday, September 9, 2018 4:27 AM
To: Eld Zierau <[email-masked]>; [email-masked]
Subject: PWID as citation (was: Suggested PWID URN for Persistent Web IDentifiers - version 3)

One feature of a citation is that it's not just an identifier for retrieving a specific instance of a resource.  If that instance is unavailable, information can be extracted from the citation that can be used to retrieve other instances of the resource.  I.e., if the cited instance is in Library A, information from the citation (author, title,
etc.) can be used to locate another instance in Library B.  The citation is *transparent* as a source of information for *partial matching* against the universe of information resources.

>From this point of view, retrieval URLs for web archives are *opaque*, at least, unless one knows the specifics of how each archive constructs its URLs.

But PWID URNs are *transparent*; the archived URL and timestamp can be extracted from the URN algorithmicly.  And those can be used to search other web archives for similar archived resources.  (Presumably, other archives don't have archived resources with exactly the same
timestamps.)

Conversely, if the archives are amenable, we can have straightforward resolution by having each archive register a URL prefix with IANA.  Like the current DOI resolver, when a URN is prefixed with its archive's URL prefix and then fetched, the referenced resource is returned.

And I think this combination of features is something new -- PWIDs could be *algorithmicly resolvable* (using their specified archives), and yet also be *citations* (transparently providing enough information that a human can find similar resources in other archives).

Dale