3 research outputs found
A Complete Characterization of Projectivity for Statistical Relational Models
A generative probabilistic model for relational data consists of a family of
probability distributions for relational structures over domains of different
sizes. In most existing statistical relational learning (SRL) frameworks, these
models are not projective in the sense that the marginal of the distribution
for size- structures on induced sub-structures of size is equal to the
given distribution for size- structures. Projectivity is very beneficial in
that it directly enables lifted inference and statistically consistent learning
from sub-sampled relational structures. In earlier work some simple fragments
of SRL languages have been identified that represent projective models.
However, no complete characterization of, and representation framework for
projective models has been given. In this paper we fill this gap: exploiting
representation theorems for infinite exchangeable arrays we introduce a class
of directed graphical latent variable models that precisely correspond to the
class of projective relational models. As a by-product we also obtain a
characterization for when a given distribution over size- structures is the
statistical frequency distribution of size- sub-structures in much larger
size- structures. These results shed new light onto the old open problem of
how to apply Halpern et al.'s "random worlds approach" for probabilistic
inference to general relational signatures.Comment: Extended version (with proof appendix) of paper that is too appear in
Proceedings of IJCAI 202
The generalised distribution semantics and projective families of distributions
We generalise the distribution semantics underpinning probabilistic logic programming by distilling its essential concept, the separation of a free random component and a deterministic part. This abstracts the core ideas beyond logic programming as such to encompass frameworks from probabilistic databases, probabilistic finite model theory and discrete lifted Bayesian networks. To demonstrate the usefulness of such a general approach, we completely characterise the projective families of distributions representable in the generalised distribution semantics and we demonstrate both that large classes of interesting projective families cannot be represented in a generalised distribution semantics and that already a very limited fragment of logic programming (acyclic determinate logic programs) in the deterministic part suffices to represent all those projective families that are representable in the generalised distribution semantics at all