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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Public identifiers and topic maps
 At 05:15 PM 9/30/98 -0500, Steven R. Newcomb wrote: >[Eliot Kimber:] > >> I think there's two different things being talked about here: > >[ ... and lots of other good stuff with which I agree.] > >But, Eliot, your note does not address the problem we're trying to >solve here. In trying to respond in depth to Steve's note, I realized what the fundamental problem is. Steve is talking about topics as though the topics were the things (i.e., the topic "Lake Geneva" *is* the actual lake). But topics are not the things, they are descriptions of and opinions about things. That's why I say that a topic is a document. We can prove that there exists in the alps of Europe a body of water that has some measurable position on the globe. That is a fact. As soon as we start saying things like "this body of water is a lake" or "this lake is called 'Lake Geneva'" we have asserted opinions about this pool of water. The opinion is not the thing. The opinion points to the thing. Topics are just formalized forms of these types of statements. They are abstract ideas that have to be documented if communication about them over any useful time scale is to occur. Why do we know that "Lake Geneva" is called "Lake Geneva"? Because someone somewhere wrote it down the assertion: this body of water to which I refer is called, by this group of people, "Lake Geneva". They created the topic "Lake Geneva" by writing down the assertion that the body of water is called "Lake Geneva" by at least one person. The topic is the idea that this body of water is called Lake Geneva, not the body of water. The document that says this is one member resource of the topic. The names of topics are not and cannot be distinguishing, in the general case, such that you can tell from two topic names whether or not the topics are the same or different. I can create a topic called "Lake Geneva" by which I mean all lakes called "Geneva" anywhere in the world. The only way you can distinguish my topic from Steve's topic is to find all the members of each topic and compare them for identity. By same token, I can create a topic with the name "That Lake in Switzerland" that is identical to Steve's topic named "Lake Geneva" (identical because it includes the same member resources). It has always been and will always be the case that if two names are the same (within the same name space, of course) then they must refer to the same resource. But the converse can never be proved: if two names are different, there's no guarantee, in the general case, that they don't refer to the same thing. You could define a name space in which you impose the rule that every resource shall have exactly one name, but then you have the problem of defining identity of resources. For things like printed books or human beings, it's relatively easy because they have lots of inherently distinguishing properties, like author, title, publisher's ISBN number, fingerprints, unique location in space and time, etc., that make it easier to inspect names to see if they might actually refer to the same thing. But topics, being more abstract (they're just ideas and opinions with no well-defined physical or electronic representation), don't have inherent distinguishing properties, so you can't use them when constructing names. It would be up to some topic cataloging service to determine when two names really referred to the same topic and disallow the cataloging of the second name. But this is a function of the catalogers, not the naming mechanism. Cheers, E. -- <Address HyTime=bibloc> W. Eliot Kimber, Senior Consulting SGML Engineer ISOGEN International Corp. 2200 N. Lamar St., Suite 230, Dallas, TX 75202. 214.953.0004 www.isogen.com </Address> xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...) 
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