1,721 research outputs found
On the Cost of Negation for Dynamic Pruning
Negated query terms allow documents containing such terms to be filtered out of a search results list, supporting disambiguation. In this work, the effect of negation on the efficiency of disjunctive, top-k retrieval is examined. First, we show how negation can be integrated efficiently into two popular dynamic pruning algorithms. Then, we explore the efficiency of our approach, and show that while often efficient, negation can negatively impact the dynamic pruning effectiveness for certain queries
Optimal quantum query bounds for almost all Boolean functions
We show that almost all n-bit Boolean functions have bounded-error quantum
query complexity at least n/2, up to lower-order terms. This improves over an
earlier n/4 lower bound of Ambainis, and shows that van Dam's oracle
interrogation is essentially optimal for almost all functions. Our proof uses
the fact that the acceptance probability of a T-query algorithm can be written
as the sum of squares of degree-T polynomials.Comment: 8 pages LaTe
Generalized Lineage-Aware Temporal Windows: Supporting Outer and Anti Joins in Temporal-Probabilistic Databases
The result of a temporal-probabilistic (TP) join with negation includes, at
each time point, the probability with which a tuple of a positive relation
matches none of the tuples in a negative relation , for a
given join condition . TP outer and anti joins thus resemble the
characteristics of relational outer and anti joins also in the case when there
exist time points at which input tuples from have non-zero
probabilities to be and input tuples from have non-zero
probabilities to be , respectively. For the computation of TP joins with
negation, we introduce generalized lineage-aware temporal windows, a mechanism
that binds an output interval to the lineages of all the matching valid tuples
of each input relation. We group the windows of two TP relations into three
disjoint sets based on the way attributes, lineage expressions and intervals
are produced. We compute all windows in an incremental manner, and we show that
pipelined computations allow for the direct integration of our approach into
PostgreSQL. We thereby alleviate the prevalent redundancies in the interval
computations of existing approaches, which is proven by an extensive
experimental evaluation with real-world datasets
Model-Checking Problems as a Basis for Parameterized Intractability
Most parameterized complexity classes are defined in terms of a parameterized
version of the Boolean satisfiability problem (the so-called weighted
satisfiability problem). For example, Downey and Fellow's W-hierarchy is of
this form. But there are also classes, for example, the A-hierarchy, that are
more naturally characterised in terms of model-checking problems for certain
fragments of first-order logic.
Downey, Fellows, and Regan were the first to establish a connection between
the two formalisms by giving a characterisation of the W-hierarchy in terms of
first-order model-checking problems. We improve their result and then prove a
similar correspondence between weighted satisfiability and model-checking
problems for the A-hierarchy and the W^*-hierarchy. Thus we obtain very uniform
characterisations of many of the most important parameterized complexity
classes in both formalisms.
Our results can be used to give new, simple proofs of some of the core
results of structural parameterized complexity theory.Comment: Changes in since v2: Metadata update
Logical and uncertainty models for information access: current trends
The current trends of research in information access as emerged from the 1999 Workshop on Logical and Uncertainty Models for Information Systems (LUMIS'99) are briefly reviewed in this paper. We believe that some of these issues will be central to future research on theory and applications of logical and uncertainty models for information access
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