[[this post never got finished but I'm having a clear-out of my drafts and they're getting published or deleted, ready or not]]
Brian Kelly just blogged [[hmm, well, back in July, I think....]] on the JISC-PoWR site about "three key aspects of web preservation": experience, information, and access. I have a fourth, but I've been using it in the context of "sustainability" (the subject of my thesis), and so first I want to say a couple of words about this vs preservation, since although I've been writing papers for Ross for a couple of years arguing about the distinction between the concepts, I've not really rehearsed this in public before.
For the last couple of years I've been arguing that the problem of sustainability (S) is distinct from that of archive-style preservation (P). I won't go into the details of the distinction here but in essence I see P as concerning the persistence of a state, and S as the persistence of a process or activity. Recent work by Chris Rusbridge and others has been blurring the boundary ever more, although in a useful way: by questioning the purpose of preservation and weighing up what are the important aspects ("significant properties") of resources, they have been starting to argue for an approach to preservation that looks a lot more like what I was previously describing as sustaining. I still sort of believe that it is useful to distinnguish between the two concepts, but there's a lot of overlap.
The aspect that I think is especially pertinent to sustaining is "purpose". I don't think this is the same as the "experience" that Brian cites Kevin Ashley on (although experience and information may feed into purpose). It's focused on the objectives of the resource, which may be attainable through radically different experiences; for example (in the case of the environment in which KA operates), the learning objectives that an educational resource was created to serve. For a museum, perhaps a resource was prepared for use in a temporary exhibition, with the objective of enriching the experience visitors to that physical space by illustrating relationships betweeen objects, and providing media resources to bring them to life. When that exhibition closes, the original objective is partially voided - there is no physical visit to enrich - but aspects of it may still be viable - the objects probably still exist and the tales about them are still worth telling, perhaps more so than ever since we've stuck them back in the store-room out of easy access. Brian was talking about web preservation, of course, and I've taken a non-web resource as an example, but my interest in the question of sustainability extends beyond the web and the point applies regardless.
In any given digital resource that we're talking about preserving/sustaining, experience and information at least (perhaps access, too, sometimes) will have contributed to the original purpose to varying degrees - sometimes the experience is the whole purpose, sometimes it's an unimportant side effect of providing access to information. And sometimes it's important to the preserver regardless of its significance to the original purpose.
So if the original purpose is no longer served by a resource, what then for our "preservation" plans? There are still often reasons to preserve (freeze) or sustain (keep alive) an application, or aspects of it - in other words, some sources of value, ranging from historical interest to new uses, which may let a resource adapt and survive. The "significant properties" idea fits in to this. For me, if you are trying to maintain some quality of the original it's more of a preservation activity; whereas if you are more fundamentally interested in continuing to extract value through maintaining utility of whatever sort, we're talking sustaining.