Saturday, December 10, 2005

StatSat is ...

Statistical Satisfiability

Using Markov Random Fields to explore issues of representation and reasoning.

SAT

Boolean Satisfiability (SAT) is the problem of finding satisfying valuations for a collection of Boolean constraints. Every set of Boolean constraints can be represented by a set of disjunctive propositional clauses.
k-SAT restricts attention to clauses with at most k literals. Every SAT problem can be reduced, by the addition of additional variables, to 3-SAT.

MRF

A Markov Random Field (MRF) determines a probability distribution over a set of random variables.
We view a MRF over a set of Boolean variables as a natural generalisation of SAT, and use a MRF to represent knowledge accumulated from experience.
We can construct a MRF, top-down a priori — for example, from a Markov Logic Network (MLN Richardson & Domingos), or bottom-up a posteriori, from a set of data.

Our bottom-up procedures are iterative and adaptive, so an initial MRF can be established to represent a priori assumptions, then adapted to reflect a posteriori experience.

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