- From: David G. Durand <dgd@cs.bu.edu>
- Date: Fri, 1 Nov 1996 13:34:25 -0500
- To: Distributed Authoring List <w3c-dist-auth@w3.org>
The real reason that referring to versions is hard is that there are some many different things that it is reasonable to do. They also interact with configuration management -- the problem of making sure that sets of linked resources are consistent and what the author wanted. In the software engineering community, the notion of composite iobjects has led to a number of distinct policies for deciding when making a new version of a part creates a new version of the whole. Hypertext complicates this again by adding links between resources. One may plausibly want at least the following sorts of links: Always current: This kind of link specifies a resource; the version of the resource must always be a unique "most up-to-date version" (according to some global config. mgt. policy). There can only be one most up-to-date version. Think of publications, where an update to one resource should invisibly propagate to all references to the resource. Always fixed: This kind of link (think editorial annotation) must always point to a specific version of a resource. It is not necessarily sensible to "forward" editorial comments to new versions of a resource/ Version consistent: This kind of link should point to the proper version of a related resource, depending on the version of the resource containing the link. (note that a link like this depends on some kind of configuration management context that associates versions of different resources with each other). Now these are all useful and they point to a fundamental fact (logically speaking). Resources are essentially indexed by their versions, which are organized as a lattice with a top element under the derived-from relation. configuration managers define maps between version trees. There are a veriety of version queries that a link could resonably make, these should be supported by URLs. Now I don't care if we hack URLs, myself, although I think that versions are integral enough to identity questions that they deserve a place in a URL or URN framework. But we need to have _some URLs_ that refer to all these types of version query (at least the three specific ones I've mentions). We can construct these URLs by URL-hacking, or we can query the server for the information, but there needs to be a way for an author do determine and use the right URI to make the links-types given above. An older, but relatively clear and easy to read hypertext paper (By Hicks, Leggett, and Schnase [TAMU HRL-91-004]), explains the basic issues of linking in the presence of versions. It's available (as Postscript, sigh) from Texas A&M's Hypermedia Research lab (Somewhere off www.bush.cs.tamu.edu). Other views can be found in several papers by Anja Haake, David Hicks, Kaspar Østerbye, Ufe Wiil, John Leggett, and others in the last 4 or 5 ACM Hypertext conference proceedings. I'm not advocating that we fix a single set of configuration management semantics -- there is not a consensus on a single right solution, or event he existence of such a solution -- but we should construct a framework within which such things cvan be constructed. Fortunately, I think we can define sufficient versioning to get the first two kinds of links I mentioned without having to commit on the large nest of snakes (oops I mean questions), involved in configuration management. -- David RE delenda est. I am not a number. I am an undefined character. _________________________________________ David Durand dgd@cs.bu.edu \ david@dynamicDiagrams.com Boston University Computer Science \ Sr. Analyst http://www.cs.bu.edu/students/grads/dgd/ \ Dynamic Diagrams --------------------------------------------\ http://dynamicDiagrams.com/ MAPA: mapping for the WWW \__________________________
Received on Friday, 1 November 1996 13:29:30 UTC