Tuesday, October 27, 2009

ISWC keynote: Pat Hayes - raw notes

Two talks in one. Blogic (web log = blog, so web logic = blogic). RDF Redux - how we could easily revise RDF to make it more expressive, without changing the meaning of existing RDF.

Principles of blogic. Web portability: logic and entailments can be accessed elsewhere, should commute. RDF is portable, ISO common logic is portable, OWL-DL, classical FOL are not. OWL-2 is better, but not quite there.

Names. IRI's have structure and meaning, can be owned and controlled, etc. However, in logic names are opaque tokens. Big disconnect, but not sure how to address it. RDF semantic interpretations are mappings from a given vocabulary, but it would be better to state 'from all possible names'

Horatio principle: truly universal quantification not a good idea. OWL is mostly OK, but complement is problematic.

SameAs not the same as. We need a way to describe co-reference without equating the conceptualisations. E.g DbPedia and CYC have different conceptualisations for sodium, but are denoted owl:sameAs.

Death by layering. Layer cake diagram is a good computer architecture layer but a really bad approach for semantics. E.g term URI's from OWL have different meanings depending on whether the triples are seen as basic RDF or as OWL.

Part 2: RDF redux

There are many things wrong with RDF that should be done better. [List]. However, there is a more basic problem: blank nodes in RDF are broken. Basic issue is that it is not obvious how to describe a bNode mathematically. Approach was to use set theory, but this was wrong. Using a Platonic idea to describe syntax. Fix would be to view graphs as drawn on some surface, then bNodes are marks on that surface. RDF redefined to be a graph + a surface, doesn't operationally change any existing RDF. No graph can be on more than one surface. Fixes lots of problems: copy vs. merge, named graphs, etc. Provides a syntactic scope for RDF nodes.

Surfaces themselves can have meaning. E.g: positive surfaces assert contents are true, negative surfaces assert contents are false, neutral surface, deprecated surface.

Would have to allow surfaces to nest, would require changes to RDF syntax. Allowing this, RDF would get full first-order semantics a la CS Pierce. Thus RDFS would not be a layer on RDF, but an abbreviation for assertions that are already expressible in (revised) RDF.

Question on tractability. Aren't the layers there for tractability? Ans: no, can still use languages with defined characteristics. Anyway layers don't do that either. This proposal is about metatheory, not practice.

Question: does it support other hard extensions like fuzzy langs, temporality? Ans: Doesn't solve, but gives it a clear point to start.

Question: (TimBL) isn't this what N3 has with curly bracket contexts? Ans: maybe, but Pierce was first

Q: so why not just fix RDF? A: would love to, what's the process?

Q: this borrows from conceptual graphs, but they aren't widely used, why would this succeed? No, just suggesting a refinement of the foundations of RDF. Don't overemphasise Pierce.

Q: we want family of nearly-same-as relations. What does logic offer? A: good question, wish I knew the ans! Context is important - success of communication depends on choosing the right interpretation of names. Lynne Stein argues this is a much more fundamental problem.

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