Deciding Definability by Deterministic Regular Expressions

International audienceWe investigate the complexity of deciding whether a given regular language can be defined with a deterministic regular expression. Our main technical result shows that the problem is Pspace-complete if the input language is represented as a regular expression or nondeterministic finite automaton. The problem becomes Expspace-complete if the language is represented as a regular expression with counters

Trade-offs in Static and Dynamic Evaluation of Hierarchical Queries

We investigate trade-offs in static and dynamic evaluation of hierarchical queries with arbitrary free variables. In the static setting, the trade-off is between the time to partially compute the query result and the delay needed to enumerate its tuples. In the dynamic setting, we additionally consider the time needed to update the query result in the presence of single-tuple inserts and deletes to the input database. Our approach observes the degree of values in the database and uses different computation and maintenance strategies for high-degree and low-degree values. For the latter it partially computes the result, while for the former it computes enough information to allow for on-the-fly enumeration. The main result of this work defines the preprocessing time, the update time, and the enumeration delay as functions of the light/heavy threshold and of the factorization width of the hierarchical query. By conveniently choosing this threshold, our approach can recover a number of prior results when restricted to hierarchical queries. For a restricted class of hierarchical queries, our approach can achieve worst-case optimal update time and enumeration delay conditioned on the Online Matrix-Vector Multiplication Conjecture.Comment: Technical Report; 52 pages. The updated version contains: new diagrams and plots summarizing known results and putting the results of the paper into context; introduction of delta_i-hieararchical queries, for any non-negative integer i; optimality results for delta_0- and delta_1-hieararchical querie

PEPPA: a project for evolutionary predator prey algorithms

The predator-prey model--based on aspects of the natural interplay of predators and prey--has become an alternative method for tackling multi-objective optimization problems. In this process, each predator targets a single objective, and it is expected that the joint influence of all predators affects the prey population in such a way that good solutions survive. This paper describes PEPPA, a modular software framework for designing and analyzing predator-prey models. It allows to model arbitrary world environments, complex predator behavior and dynamic prey adaptation. Further, PEPPA provides various tools for modeling, visualization and parallelization. We explain the architecture and handling of the framework and provide exemplary results on a simple multi-objective benchmark problem

Deciding definability by deterministic regular expressions

International audienceWe investigate the complexity of deciding whether a given regular language can be defined with a deterministic regular expression. Our main technical result shows that the problem is Pspace-complete if the input language is represented as a regular expression or nondeterministic finite automaton. The problem becomes Expspace-complete if the language is represented as a regular expression with counters

Deciding Definability by Deterministic Regular Expressions

International audienceWe investigate the complexity of deciding whether a given regular language can be defined with a deterministic regular expression. Our main technical result shows that the problem is Pspace-complete if the input language is represented as a regular expression or nondeterministic finite automaton. The problem becomes Expspace-complete if the language is represented as a regular expression with counters

Deciding Definability by Deterministic Regular Expressions

International audienceWe investigate the complexity of deciding whether a given regular language can be defined with a deterministic regular expression. Our main technical result shows that the problem is Pspace-complete if the input language is represented as a regular expression or nondeterministic finite automaton. The problem becomes Expspace-complete if the language is represented as a regular expression with counters