Archive of UserLand's first discussion group, started October 5, 1998.

Re: What is RDF?

Author:Paul Snively
Posted:8/22/2000; 8:08:26 AM
Topic:What is RDF?
Msg #:19918 (In response to 19914)
Prev/Next:19917 / 19919

David Carter-Tod: Is there anywhere that I can get an explanation of all this? To my mind, this is the problem with RDF. I'm averagely smart and I don't understand a word of what this means. That's not to say it's not important, but where's the one page explanation of each of these terms:

Logical rules: seems to be being used in a different way from everyday use

I'm not sure in what sense you feel the use of the phrase "logical rules" here differs from everyday use, apart from being expressed in a (formal) written language. In any case, a good primer on the First Order Predicate Calculus, the "logic" that is almost certainly being referred to, can be found at <http://cbl.leeds.ac.uk/~paul/prologbook/node18.html>.

David: Ontologies: ditto

"Ontologies" in this context (as opposed to a philosophy-based context) simply refers to a collection of facts and rules taken as an aggregate. Loosely speaking, an ontology is "that which can be known," which does map pretty directly to the literal meaning of the word "ontology," but it's still AI jargon, no question.

David: Inference rules/inferencing: ditto

For any logic, there is a (hopefully small) set of rules that govern how, given a set of assertions and logical rules, you can generate new assertions. These rules frequently have odd-sounding names, like "Modus Ponens," "Modus Tollens," "DeMorgan's Theorem," and the like. "Inferencing" is exactly what you think it is: inferring a conclusion from a set of premises by following a set of (hopefully valid) inferencing rules. We all do it every day; we probably just don't reflect on the process unless we are a logician or philosopher or AI researcher.

David: Representations with declarative semantics:?

As opposed to procedural. "Declarative semantics" talk about the world in terms of "what is" and "what's wanted;" "procedural semantics" talk about the world in terms of "how to" and "by what means." To put this in somewhat more concrete terms, one of the reasons that the SQL language for database manipulation has been considered such a success is because it is declarative rather than procedural; you SQL query says what you are looking for and does not need to specify how to find it. That is the job of the query optimizer and query engine.

David: DAML:?

<http://www.daml.org/>

David: It appears that all these terms are being used in a technical sense, but their everyday use does not have a technical meaning.

I would disagree with this as stated, but would merely reformulate it as "It appears that all these terms are being used in a formal sense, but their everday use is sufficiently informal as to make the formal use unintuitive," a variant of what you said that I would agree with.

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