Thursday, September 25, 2003

The Transient and the Permanent

Time was, a URL was a concrete pointer to a resource. Because it built on DNS, the machine could move to a new network, but the URL was "guaranteed" (in a meaning of the word guarantee very unlike that in normal discourse) to remain the same. For example, if you were publishing a paper, and you wanted readers who might be looking at a hard copy to be able to find updates, you might include the URL.

I just read a paper (Philip Wadler's Call-By-Name Is Dual to Call-By-Value) in which the author says that you can find the original home of the paper by "gooling wadler dual." Now it's not hard to understand why Wadler, who has had as employers recently AT&T, Lucent, and Avaya without changing his job once, would not trust a URL built on the current name of his employer to remain valid. But I think it's a sign of a larger and more interesting trend.

Back when URLs were presumed permanent, search was a very approximate mapping over those URLs. And, as search technology improved and changed by lurches and fits, no two searches were really guaranteed to return the same results. However, Google, with its social-network-baked-in algorithms, has changed the analysis. For fairly important documents, a carefully selected set of keywords (wadler, dual being otherwise fairly unlikely) will if not uniquely, at least reliably, return the wished-for page. Now, URLs are transient, as we move from company to company or ISP to ISP; it is search that is, more or less, permanent.

Now the interesting test will be to see if this page that I'm writing right now climbs very high. I have, after all, repeated "wadler dual" quite a number of times. (Of course, I've pointed at the paper URL myself, so as long as Avaya is Avaya, finding this page is almost as good.)