On Jul 15, 2007, at 1:53 PM, Eric Jain wrote:
imagine you want to make some statements about http:// www.ebi.uniprot.org/entry/P12345, one of the current pages. If you note down the time you accessed this page, you may still be able to retrieve the representation you described in future, e.g. courtesy of the Wayback Machine. But if all you have is a PURL, bad luck!
Two points to make about this. First, the current locations are not hidden - the rewrite rules are accessible, and the agent that follows the redirect can note the actual location.
Second, how are we to know that this page changes over time, and that we might need to protect ourselves. Making this sort of knowledge available to our agents is another important piece of the puzzle. LSIDs had a single policy identifying that the "data" portion never changes. We've found over time that while this policy works for some cases, it doesn't work for all. I've suggested that we need to define a set of policies that reflect the actual practices and associate a policy with each resource. In order to not box ourselves in, it is desirable that there is an extension mechanism for the policy set so that if new policies become useful we have a way to make agents aware of them.
-Alan
