Saturday, March 18, 2006
Friday, March 17, 2006
Now, this is not all that abstruse, but then I have a math degree and am used to it. Way back then I studied mathematical logic, thought it was fun but a lousy way to describe the world and a lousy model for computation. It seems to have triumphed, however, and now people are expected to speak that language (the RDF semantics spec is even worse). I have a hard time believing that working programmers (a set of which I myself am a member of, nowadays) are going to be gleefully soaking up all the model-theoretic semantic theory behind the semantic web.
A basic graph patterns is a set of triple patterns and forms the basis of SPARQL query matching. Matching a basic graph pattern is defined in terms of generic entailment to allow for future extension of the language.
Definition: E-entailment Regime
An E-entailment regime is a binary relation between subsets of RDF graphs.
A graph in the range of an E-entailment is called well-formed for the E-entailment.
This specification covers only simple entailment [RDF-MT] as E-entailment. Examples of other E-entailment regimes are RDF entailment [RDF-MT], RDFS entailment [RDF-MT], OWL entailment [OWL-Semantics].
Definition: Basic Graph Pattern equivalence
Two basic graph patterns are equivalent if there is a bijection M between the terms of the triple patterns that maps blank nodes to blank nodes and maps variables, literals and IRIs to themselves, such that a triple ( s, p, o ) is in the first pattern if and only if the triple ( M(s), M(p) M(o) ) is in the second.
This definition extends that for RDF graph-equivalence to basic graph patterns by preserving variables names across equivalent graphs
Maybe I'm wrong, there are people willing to boil things down into understandability. This well-written article doesn't cover any sort of non-trivial queries however.
There seems to be a big gap between RDF-as-first-order-predicate-logic-with-model-theoretic-semantics and RDF-as-useful-flexible-emerging-data-standard. Looked at positively, it's a two-pronged thrust, from academia and hackerdom acting together.
Wednesday, March 15, 2006
I guess I don't like fundamentalisms of any sort. Libertarianism and atheism both tend to be all-explanatory and ignorant of nuance. Libertarianism in its fascination with the distributed market model ignores anything which doesn't fit its framework, such as public goods, distortion of the market by the overly powerful (who can manipulate it unfairly) and the poor (who may have no motivation to respect property rights). Atheism tends to ignore the nature of religious belief, treating as something like bad science, rather than trying to understand what it might really be about. Let's just say God is the referent of the word "God", and while it may not exist the way a chair exists, it has a real conceptual role in thought which it might be useful to understand.
Tuesday, March 14, 2006
The Semantic Web standards are complex, verbose, and hard to understand. They are backed by Web programmers prefer simpler standards: REST over SOAP, folksonomies over ontologies. Web guys do mashups and go to ETech; semantic technologists propose complex architectures and require large funders to get them realized.
It surprises me but it looks like the pressure of hard problems with good funding will overcome the complexity barrier of the Semantic Web. It surprises me not even so much because the syntaxes are complex and verbose, but the results are fairly inexpressive and inflexible in certain ways (for instance, OWL, the ontology standard, is based on description logic which makes it hard to do something as simple as default reasoning, something any simple old-fashioned frame system could do). Having been out of industrial grade AI for awhile, I will reserve judgement.
Sunday, March 05, 2006
There is actually some pretty interesting stuff going in this space, especially in life science, and an awful lot of coporate hype. I will be attempting to separate out the two.