Thursday, April 22, 2021

What Is The Point?

During a discussion of NFTs, Larry Masinter pointed me to his 2012 proposal The 'tdb' and 'duri' URI schemes, based on dated URIs. The proposal's abstract reads:
This document defines two URI schemes.  The first, 'duri' (standing
for "dated URI"), identifies a resource as of a particular time.
This allows explicit reference to the "time of retrieval", similar to
the way in which bibliographic references containing URIs are often

The second scheme, 'tdb' ( standing for "Thing Described By"),
provides a way of minting URIs for anything that can be described, by
the means of identifying a description as of a particular time.
These schemes were posited as "thought experiments", and therefore
this document is designated as Experimental.
As far as I can tell, this proposal went nowhere, but it raises a question that is also raised by NFTs. What is the point of a link that is unlikely to continue to resolve to the expected content? Below the fold I explore this question.

I think there are two main reasons why duri: went nowhere:
  • The duri: concept implies that Web content in general is not static, but it is actually much more dynamic than that. Even the duri: specification admits this:
    There are many URIs which are, unfortunately, not particularly
    "uniform", in the sense that two clients can observe completely
    different content for the same resource, at exactly the same time.
    Personalization, advertisements, geolocation, watermarks, all make it very unlikely that either several clients accessing the same URI at the same time, or a single client accessing the same URI at different times, would see the same content.
  • When this proposal was put forward in 2012, it was competing with a less elegant but much more useful competitor that had been in use for 16 years. The duri: specificartion admits that:
    There are no direct resolution servers or processes for 'duri' or
    'tdb' URIs.  However, a 'duri' URI might be "resolvable" in the sense
    that a resource that was accessed at a point in time might have the
    result of that access cached or archived in an Internet archive
    service.  See, for example, the "Internet Archive" project
    But the duri: URI doesn't provide the information needed to resolve to the "cached or archived" content. The Internet Archive's Wayback Machine uses URIs which, instead of the prefix duri:[datetime]: have the prefix[datetime]/. This is more useful, both because browsers will actually resolve these URIs, and because they resolve to a service devoted to delivering the content of the URI at the specified time.
The competition for duri: was not merely long established, but also actually did what users presumably wanted, which was to resolve to the content of the specified URL at the specified time.

It is true that a user creating a Wayback Machine URL, perhaps using the "Save Page Now" button, would preserve the content accessed by the Wayback Machine's crawler. which might be different from that accessed by the user themselves. But the user could compare the two versions at the time of creation, and avoid using the created Wayback Machine URL if the differences were significant. Publishing a Wayback Machine URL carries an implicit warranty that the creator regarded any differences as insignificant.

The history of duri: suggests that there isn't a lot of point in "durable" URIs lacking an expectation that they will continue to resolve to the original content. NFTs have the expectation, but lack the mechanism necessary to satisfy the expectation.

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