- From: Murray Altheim <altheim@eng.sun.com>
- Date: Tue, 10 Apr 2001 15:14:46 -0700
- To: "Charles F. Munat" <chas@munat.com>
- CC: www-rdf-interest@w3.org
"Charles F. Munat" wrote: > > Some types of resources on the Web are volatile by nature. John Doe puts up > a personal web page. Three weeks later, he decides he doesn't really want a > personal Web page - too much trouble to update it - and deletes it. > > It seems to me that there are some resources that *should* be persistent, > others that have no need to be. Has anyone given any thought to how to > distinguish the two? Should RDF mark persistent documents as such? Should > anything not so marked be presumed to be volatile? Are there different > degrees of persistence (e.g., a page that is persistent while some of the > data on the page changes, or a page that represents the latest version of a > document - but always that document). > > What about the way in which these documents are referenced. Would it be > better to have both permanent and temporary links? Could links be set to > expire? Could documents include an expire date and links to that document > automatically expire when the document did? Obviously, stability and longevity are relative and subjective terms. Some would consider one year, some five, some one hundred as a stable time period. This varies by individual, community, and application. Rather than try to navigate that particular thorn patch, XTM [1] leaves this up to the author. If as a topic map author I am trying to create identifiers that I want people to use as such, I advertise them not simply as URIs but as Published Subject Indicators (PSIs) [2], which means that I intend them as stable indicators. I might publish a list of PSIs in a specification, an online or print trade journal. These identifiers could be used in my community and would have whatever stability I claim. Life is unpredictable, but differentiating a URI as a PSI means that I intend them as identifiers. Obviously, my publication of a PSI is different than say, the US Library of Congress. But that's what we call "competition in the marketplace", eh? In my work with the Cyc ontology [3] one of the first things I endeavoured to do was ascertain how stable the HTML documentation for Cyc 2.1 was, and contacted Doug Lenat in this regard. Upon his reassurance I published a set of "canonical" URIs that can be used as PSIs to indicate Cyc constants in the upper ontology. These have been published as a list [4] and can be used today. Neither I nor Doug will change the list for Cyc version 2.1. We may at some point in the future need to topic-map the relations between the current list and some newer version, but the point I'm trying to make is that absent any true legal contract one *never* has a guarantee of stability. That doesn't inhibit the use of URIs as identifiers, unless one expects a specific result upon resolution. Amazon.com, the W3C and even IBM might not be around in ten years, but the identifiers still will identify the same things as the day they were first published, and are thus useful. Your question addresses more specifically resources, and you correctly point out that there's little that can be done to guarantee their stability. You touch upon many of the outstanding challenges in IT, and I'm encouraged by the ability of technologies such as RDF and XTM to be able to represent things like confidence levels, expirations dates, etc. outside of the resources themselves. These problems don't go away via RDF or XTM, but certainly seem more manageable simply because there is a standardized methodology to provide metadata about resources and now map it into existing ontologies and topologies. Murray [1] http://www.topicmaps.org/xtm/1.0/ [2] http://www.topicmaps.org/xtm/1.0/#desc-psis [3] http://www.doctypes.org/cyc/cyc-xtm-20010227.html [BTW, this is very much a work-in-progress] [4] http://www.doctypes.org/cyc/constants.html ........................................................................... Murray Altheim, SGML/XML Grease Monkey <mailto:altheim@eng.sun.com> XML Technology Center Sun Microsystems, 1601 Willow Rd., MS UMPK17-102, Menlo Park, CA 94025 the wood louse sits on a splinter and sings to the rising sap ain't it awful how winter lingers in springtimes lap -- archy
Received on Tuesday, 10 April 2001 18:12:44 UTC