diff --git a/abstract.tex b/abstract.tex index c5237e8..f25d56b 100644 --- a/abstract.tex +++ b/abstract.tex @@ -1,11 +1,15 @@ %root: main.tex %!TEX root=./main.tex \begin{abstract} - The problem of computing the marginal probability of a tuple in the result of a query over set-probabilistic databases (PDBs) can be reduced to calculating the probability of the \emph{lineage formula} of the result, a Boolean formula over random variables representing the existence of tuples in the database's possible worlds. - The analog for bag semantics is a natural number-valued polynomial over random variables that evaluates to the multiplicity of the tuple in each world. - In this work, we study the problem of calculating the expectation of such polynomials (a tuple's expected multiplicity) exactly and approximately. +% The problem of computing the marginal probability of a tuple in the result of a query over set-probabilistic databases (PDBs) can be reduced to calculating the probability of the \emph{lineage formula} of the result, a Boolean formula over random variables representing the existence of tuples in the database's possible worlds. + The problem of computing the marginal probability of a tuple in the result of a query over set-probabilistic databases (PDBs) is arguably the most fundamental problem in set-PDBs. +%can be reduced to calculating the probability of the \emph{lineage formula} of the result, a Boolean formula over random variables representing the existence of tuples in the database's possible worlds. + %The analog for bag semantics is a natural number-valued polynomial over random variables that evaluates to the multiplicity of the tuple in each world. + The analog for bag semantics is computing the expected multiplicity of a result tuple. + %In this work, we study the problem of calculating the expectation of such polynomials (a tuple's expected multiplicity) exactly and approximately. + In this work, we study the problem of a tuple's expected multiplicity exactly and approximately. We are specifically interested in the fine-grained complexity of this problem relative to the complexity of deterministic query evaluation --- if these complexities are comparable, it opens the door to practical deployment of probabilistic databases. - Unfortunately, we show the reverse; our results imply that computing probabilities for Bag-PDB based on the results produced by such algorithms introduces super-linear overhead. + Unfortunately, we show the reverse; our results imply that computing expected multiplicities for Bag-PDB based on the results produced by such algorithms introduces super-linear overhead. % Such factorized representations are necessary to realize the performance of modern join algorithms (e.g., worst-case optimal joins), and so our results imply that a Bag-PDB doing exact computations (via these factorized representations) can never be as fast as a classical (deterministic) database. The problem stays hard even if all input tuples have a fixed probability $\prob$ (s.t. $\prob \in (0,1)$). We proceed to study polynomials of result tuples of positive relational algebra queries ($\raPlus$) over TIDBs and for a non-trivial subclass of block-independent databases (BIDBs).