2005-06-15

Ontology Mapping, Ineffable Subjects and Blank Nodes

In this thread on SWAD forum, Alistair Miles and Dan Brickley re-activate an old issue : How do I express that resource X in representation scheme A (e.g. a SKOS concept scheme) and resource Y in representation scheme B (e.g. an OWL ontology) are somehow representations of the same (----) . After suggesting a suboptimal Topic Map solution I suddenly yesterday came out with the idea that in RDF, blank nodes could be a killer solution. Actually one can use blank nodes to aggregate various representations of whatever, keeping agnostic on what this whatever is. Using blank nodes to represent "ineffable subjects" is cool, since nobody is able to say anything directly about them (asserting name, type or any other property), since they have no URI. Put it together with recent debate on ISO SC34 mailing list about subject locators, and consider this provocative conclusion : RDF blank nodes are better than TM topics at representing subjects, since, and this is my last thought, subjects have no identity, only representations have one. Subjects have no identity, read no type, no property at all. Resources have identity (URIs), so the best attempt to indicate a subject is to gather various resources in a blank node, as so many fingers pointing towards the moon.
Remember in the Topic Maps book, I wrote about an empty subject indicator ...

2 comments:

  1. A useful restatement of the original issue is found here following a really interesting series of discussions that are referenced in this post.

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  2. I insist that subjects do have identity, but only within contexts -- within universes of discourse. That's as true for subjects that are expressions as it is for subjects that are not expressions.

    I can see how, in implementations of systems that create proxies for subjects, blank nodes can serve various purposes. In Versavant, for example, proxyObject objects can (and must) be created before they can be given subject identity properties (SIPs) that, within the disclosed contexts that govern them, establish the subjects for which proxyObjects are proxies. But I don't see how it's meaningful to say that a proxy is not a proxy for something in particular. By its very nature, a proxy is always a proxy for something in particular.

    Last time I spoke with Bernard about this kind of thing, he was accusing me -- in the friendliest and most agreeable fashion imaginable -- of some sort of religious Platonism that necessitates the absolute existence of subjects independent of their expressions. I, in an equally friendly way, was accusing him of assuming a position that, in the final analysis, denies the possibility of communication, by denying any absolute value to symbols. It is ironic and perhaps predictable that I now find myself once again in dialectic tension with my dear friend, whose intellectual honesty and clarity I admire greatly, BTW. These days, I'm saying that the values of symbols (i.e., the subjects that symbols represent) are very real within their (possibly various) context(s), while Bernard is proposing that subjects have no identities, only representations (symbols, proxies for subjects) have identities. There is truth behind what he says, but I would ask him whether God Herself has identity, or has existence, and/or is an expression. (;^)

    At the risk of offending many, I would also like to take this opportunity to disparage philosophies that deny the value of what the present and previous Popes called "relativism". If world peace is achievable at all, one of its hallmarks will be respect for the diversity of the contexts within which subjects have their existence. Truth is 100% relative to context, and anybody who hasn't noticed that there are multiple contexts is either very young or hasn't been paying attention.

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