My last two posts were motivated by Sean McGrath’s piece on URLs and the social contracts they imply. So, too, this one.
Sean argues for the network-value of a naming convention for URLs, namely, the inclusion in URLs-of-permanent-intent of the string ‘purl’. When I first read his post, my egocentrism led me to think he was alluding to the PURL system, launched by OCLC a dozen years ago in response to our frustrations with the ground-hog-day character of the URN meetings in the IETF. We launched PURLs with an expectation that they would be widely adopted and deployed by all right-thinking Web managers (we had a LOT of silly ideas like that…). PURLs have never been as widely deployed as were our hopes, but they are still alive and growing, and remain both useful and an instructive data point in the evolution of the Internet naming architecture.
One reason I was so ready to conclude that Sean was talking about PURLS is his argument:
I am thinking of nothing more complicated than a social naming convention. What if permanent URLs contained the fragment '/purl/' for example? Would that not do the trick? As a consumer, I look at example.com/purl/info12.html and can immediately infer that it is a good candidate for bookmarking.
From a URL consumer's perspective, this would be very handy I think. From a URL producer's perspective, it would also be very handy. In effect, it would allow URL producers to send out signals to the world. One signal would be: 'this URL is a good bookmark candidate. We won't be changing it and even if we change our systems internally, we will make every effort to ensure that this link will continue to work.'. The second signal would be 'This URL is not a good bookmark candidate. Bookmark it at your own risk.' Simply leaving '/purl/' out of a URL would send the latter signal.
No new technology added! An approach predicated on the URL-equivalent of a smilie, a token that says that someone is looking after this identifier. It is an important component of the added-value that we envisioned for PURLs, as it happens. People will see http://purl.og/.... and say... hey, a URL for the long haul. OK… we’re not exactly talking a firestorm of adoption. But the point was true then and true today.
Back to permanence and persistence. As I harbored the delusional notion that Sean was singing about our PURLy fates, I thought… “oh… he got the P part wrong (invoking the word permanent rather than persistent)” It would appear, in fact, that he had arrived independently at a related acronym.
The distinction is small, but important. What can permanence mean in a technological world where only one of twenty students in a masters level information science class recognized the phrase NCSA Mosaic? (Well, it means that change is unrelenting and they don’t listen to big band music much either). And follow this link (top of the Google search set), if you think I'm blowing smoke:
NCSA Mosaic Home Page
Creation and history of the browser. All versions available for download.
I feel unlucky.
Even in the hallowed halls of LibraryLand, we are (justly) reluctant to talk about preservation in terms longer than the odd millennium. Much of the discussion surrounding business models for digital preservation has to do with service contracts and the cost of assuring the integrity of a given bitstream for a given interval. It is NOT permanence we’re talking about. It is persistence. And the definition refers to a business process more than it does to a point in the past or future.
If you have an identifier used for tracking the progress of a laptop from its point of manufacture in Shanghai to your doorstep, the business process that is identified (a shipment of a consumer good) is concluded in a period measured in hours or days (mine took 40 hours). Soon after, the identifier is so much digital chaff, duty done. But certainly persistent in the context of its intended use.
If we’re talking about cultural heritage assets, we have expectations measured in centuries. In either case, the success of the identifier is tied to the life cycle of the asset or process, not to a calendar. Thinking of our identifiers in these terms helps avoid staring towards a vanishing point. Sometimes.