Acta Informatica
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Querying sequence databases with transducers
Acta Informatica - Tập 36 - Trang 511-544 - 2000
This paper develops a database query language called Transducer Datalog motivated by the needs of a new and emerging class of database applications. In these applications, such as text databases and genome databases, the storage and manipulation of long character sequences is a crucial feature. The issues involved in managing this kind of data are not addressed by traditional database systems, ei......
Probabilistic models of computer systems
Acta Informatica - Tập 12 - Trang 285-303 - 1979
In this paper we examine certain problems related to the use of diffusion approximations for the approximate modelling of computer systems. In particular we develop a model which allows us to handle waiting times and batch arrivals: these results are a new approach to the use of diffusion approximations. We also examine the effect of the distribution of holding times at boundaries: this question h......
On Gurevich's theorem on sequential algorithms
Acta Informatica - Tập 39 - Trang 273-305 - 2003
Abstract-State Machines have been introduced as “a computation model that is more powerful and more universal than standard computation models”, by Yuri Gurevich in 1985. ASM gained much attention as a specification method, in particular for the description of the semantics of programming languages, communication protocols, distributed algorithms, etc. Gurevich proved recently that a sequential a......
Subsequence versus substring constraints in sequence pattern languages
Acta Informatica - Tập 58 - Trang 35-56 - 2019
A family of logics for expressing patterns in sequences is investigated. The logics are all fragments of first-order logic, but they are variable-free. Instead, they can use substring and subsequence constraints as basic propositions. Propositions expressing constraints on the beginning or the end of the sequence are also available. Also wildcards can be used, which is important when the alphabet ......
A theory of ultimately periodic languages and automata with an application to time granularity
Acta Informatica - Tập 46 - Trang 331-360 - 2009
In this paper, we develop a theory of regular ω-languages that consist of ultimately periodic words only and we provide it with an automaton-based characterization. The resulting class of automata, called ultimately periodic automata (UPA), is a subclass of the class of Büchi automata and inherits some properties of automata over finite words (NFA). Taking advantage of the similarities among UPA, ......
Enhanced prefetching and caching strategies for single- and multi-disk systems
Acta Informatica - Tập 42 - Trang 21-42 - 2005
We study integrated offline caching and prefetching algorithms both in the single- and the multi-disk case. For the problem of minimizing the execution time of a given request sequence, we present simple algorithms. In the single-disk case we present a combinatorial algorithm with an approximation ratio of 3/2. An optimal solution can be computed using a linear program but this requires a very lar......
Reduction rules for time Petri nets
Acta Informatica - Tập 33 - Trang 687-706 - 1996
The goal of net reduction is to increase the effectiveness of Petri-netbased real-time program analysis. Petri-net-based analysis, like all reachabilitybased methods, suffers from the state explosion problem. Petri net reduction is one key method for combating this problem. In this paper, we extend several rules for the reduction of ordinary Petri nets to work with time Petri nets. We introduce a ......
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