http://norman.walsh.name/2006/09/05/identifiers 9 84 2006-09-05T11:39:32-04:00 $Date: 2006-09-05 15:03:07 -0400 (Tue, 05 Sep 2006) $ Norman Walsh 2006 Norman Walsh More thoughts on identifiers. Names, that is, and addresses, of course. [This essay is effectively part of a conversation. You're more likely to find it understandable if you've read my earlier piece, Names and addresses, and Stuart Weibel ’s follow-up essays, starting with On Identifiers, Scholarship, and Spitoons. —ed] Stuart Weibel responded at length to my latest posting about names and addresses. Happily, we seem to be largely in agreement. The most significant point of disagreement, I think, is over the value of what Stuart calls “pure identifiers”. That is, identifiers that are intentionally and explicitly decoupled from any resolution mechanism. Part of this disagreement clearly stems from different understandings about what it means to use an http URI. Using an http URI does not require deployment of a web server or obligate the user to provide representations for the identifiers created. It's definitely desirable and useful to do so, but it isn't required. That's simply a fact. Arguments against http URIs based on the cost or inconvenience of maintaining web infrastructure to support access to those URIs don't hold water. I accept that there are some issues of user expectation here, but I don't find those issues sufficient to warrant the invention or use of “pure identifiers”. In particular, I observe that not deploying a web server for your http URIs today doesn't preclude you from doing so tomorrow. So an organization might decide that some of its identifiers had gained such broad use that there was value in supporting access to them. That general observation aside, Stuart makes some specific arguments in favor of pure identifiers: His first argument is that they are valuable for things that are conceptual, in particular, to identify things that are language independent and have different meanings in different cultural contexts. He gives, as an example, two books with the same Dewey Decimal number, 959.7043: Vietnamese War, 1961-1975 DDC/22/eng//959.7043 (English language version of DDC 22) American War, 1961-1975 DDC/22/vie//959.7043 (Vietnamese language version of DDC 22) and observes that “the distance between the abstractions rendered in two languages is greater than mere translation.” Unfortunately, I think his further argument that “what this identifier should resolve to is complicated and context dependent”, arises because he's changed the question in mid-stream. “Which book does the user want?” isn't the right question. The right question is, what does “959.7043” identify? As near as I can tell, the answer to that question is entirely independent of language and cultural context: the Dewey Decimal number 959.7043 identifies the concept of the Vietnam War. For that concept, I assert that http://xmlns.com/wordnet/1.6/Vietnam_war is an equally good identifier. Superior, in fact, because if I do a GET on that resource I find that it's about “a prolonged war (1954-1975) between the communist armies of North Vietnam who were supported by the Chinese and the non-communist armies of South Vietnam who were supported by the United States” whereas I had to rely on Google and heuristics to determine that that's what 959.7043 is most likely about. Stuart next argues for pure identifiers for legacy assets. He gives ISBN numbers as an example, but I think the isbn: scheme is an historical accident as much as anything else. Given a legacy identifier, “12345”, there are a few of ways to imagine making a URI out of it. One is “legacy-identifier-scheme:12345”. Another is “http://legacy-identifier.org/12345”. I don't see any advantage of the former over the latter. (With respect to ISBN numbers in particular, I observe that they identify a non-intuitive resource. That resource is the set of all books that have ever had that ISBN number. At least, that's the only interpretation of an ISBN number that makes sense to me.) Finally, Stuart argues that there are business cases for late-resolution-binding of identifier resolution. Perhaps. Unfortunately, I don't think I really understand the examples given. One thread seems to to be about access control, the argument apparently being that newscheme:something is better because the resolution mechanism for that URI can manage whether or not the user has authority to access that resource. But authority is an entirely orthogonal issue. There are several ways to limit access to http://example.com/something. There may be circumstances under which there are compelling reasons not to use http URIs, but no such circumstances have yet been convincingly articulated to me.