26,058 research outputs found
Reasoning about embedded dependencies using inclusion dependencies
The implication problem for the class of embedded dependencies is
undecidable. However, this does not imply lackness of a proof procedure as
exemplified by the chase algorithm. In this paper we present a complete
axiomatization of embedded dependencies that is based on the chase and uses
inclusion dependencies and implicit existential quantification in the
intermediate steps of deductions
Distribution Constraints: The Chase for Distributed Data
This paper introduces a declarative framework to specify and reason about distributions of data over computing nodes in a distributed setting. More specifically, it proposes distribution constraints which are tuple and equality generating dependencies (tgds and egds) extended with node variables ranging over computing nodes. In particular, they can express co-partitioning constraints and constraints about range-based data distributions by using comparison atoms. The main technical contribution is the study of the implication problem of distribution constraints. While implication is undecidable in general, relevant fragments of so-called data-full constraints are exhibited for which the corresponding implication problems are complete for EXPTIME, PSPACE and NP. These results yield bounds on deciding parallel-correctness for conjunctive queries in the presence of distribution constraints
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An Overview of Models for Response Times and Processes in Cognitive Tests.
Response times (RTs) are a natural kind of data to investigate cognitive processes underlying cognitive test performance. We give an overview of modeling approaches and of findings obtained with these approaches. Four types of models are discussed: response time models (RT as the sole dependent variable), joint models (RT together with other variables as dependent variable), local dependency models (with remaining dependencies between RT and accuracy), and response time as covariate models (RT as independent variable). The evidence from these approaches is often not very informative about the specific kind of processes (other than problem solving, information accumulation, and rapid guessing), but the findings do suggest dual processing: automated processing (e.g., knowledge retrieval) vs. controlled processing (e.g., sequential reasoning steps), and alternative explanations for the same results exist. While it seems well-possible to differentiate rapid guessing from normal problem solving (which can be based on automated or controlled processing), further decompositions of response times are rarely made, although possible based on some of model approaches
Naming the Pain in Requirements Engineering: A Design for a Global Family of Surveys and First Results from Germany
For many years, we have observed industry struggling in defining a high
quality requirements engineering (RE) and researchers trying to understand
industrial expectations and problems. Although we are investigating the
discipline with a plethora of empirical studies, they still do not allow for
empirical generalisations. To lay an empirical and externally valid foundation
about the state of the practice in RE, we aim at a series of open and
reproducible surveys that allow us to steer future research in a problem-driven
manner. We designed a globally distributed family of surveys in joint
collaborations with different researchers and completed the first run in
Germany. The instrument is based on a theory in the form of a set of hypotheses
inferred from our experiences and available studies. We test each hypothesis in
our theory and identify further candidates to extend the theory by correlation
and Grounded Theory analysis. In this article, we report on the design of the
family of surveys, its underlying theory, and the full results obtained from
Germany with participants from 58 companies. The results reveal, for example, a
tendency to improve RE via internally defined qualitative methods rather than
relying on normative approaches like CMMI. We also discovered various RE
problems that are statistically significant in practice. For instance, we could
corroborate communication flaws or moving targets as problems in practice. Our
results are not yet fully representative but already give first insights into
current practices and problems in RE, and they allow us to draw lessons learnt
for future replications. Our results obtained from this first run in Germany
make us confident that the survey design and instrument are well-suited to be
replicated and, thereby, to create a generalisable empirical basis of RE in
practice
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