The HTTP protocol specification describes URLs as the means by which one Web resource can refer to another resource. In a recent blog post, On Linking, Tim Bray points out that in the way the Web evolved, instead of linking to a single resource, we would be better off linking to a set of Web resources instead.

One reason: Links on the Web are often not permanent, hence the durability of a single URL reference cannot be taken for granted. A link-bundle, instead, would make links more useful in the long term.

To put this issue in context, Bray compares the ephemeral nature of links on the Web to the relative permanence of references in print publishing:

The word “scholarly” applies to work in which no assertion may stand unaccompanied by supporting evidence; I think scholarly is good... Academic citations, the stuff of scholarship, are not simple one-way pointers, they are little bundles of metadata: a page (or section) number in a particular edition of a particular published work, identified by author, title, date, publisher, and so on. Given the way the library system works, there’s a high degree of confidence that, given the contents of a citation, you’ll be able to track down the original.

Web links are clearly transient and fragile by comparison (the appeal of linking to Wikipedia is precisely that, at the moment, it feels a little less so). On the other hand, you can click on them and follow them, right here right now; and you can spin “transient and fragile” the other way, as “dynamic and fresh”. I don’t think, on balance, that they’re a step backward.

Bray suggests that a solution to this problem is to link not to a single resource, but to a set of Web resources:

If we really care about links being useful in the long term (and we should), maybe we need to abandon the notion that a single pointer is the right way to make one that matters.

If I want to link to Accenture or Bob Dylan or Chartres Cathedral, I can think of three plausible ways: via the “official” sites, the Wikipedia entries, and Google searches for the names. [More generally, I should say: direct links, online reference-resource links, and search-based links.]

What I want, then, is a link to a bunch of things at once. It turns out that there’s a perfectly good, if lightly-implemented, way to do this in XML, called XLink... [Editor's note: XML Linking Language, Version 1.0]. It’s been lightly-implemented mostly I think because the browser writers just didn’t feel any particular pull for such a thing. This has struck me as a little odd because every financial Web site in the world is full of multi-ended links: every time they mention a company they’ll typically link to its share price, some analysis, and previous articles.

How do you solve the link permanence problem in your applications?