Acta Informatica最新文献

Interface theories based on Interface Automata (IA) are formalisms for the component-based specification of concurrent systems. Extensions of their basic synchronization mechanism permit the modelling of data, but are studied in more complex settings involving modal transition systems or do not abstract from internal computation. In this article, we show how de Alfaro and Henzinger’s original IA theory can be conservatively extended by shared memory data, without sacrificing simplicity or imposing restrictions. Our extension IA for shared Memory (IAM) decorates transitions with pre- and post-conditions over algebraic expressions on shared variables, which are taken into account by IA’s notion of component compatibility. Simplicity is preserved as IAM can be embedded into IA and, thus, accurately lifts IA’s compatibility concept to shared memory. We also provide a ground semantics for IAM that demonstrates that our abstract handling of data within IA’s open systems view is faithful to the standard treatment of data in closed systems.

We formalize several regular numeral systems, state their properties and supported operations, clarify the correctness, and tabulate the proofs. Our goal is to use as few symbols in the presentation of digits and make as few digit changes as possible in every operation. Most importantly, we introduce two new systems: (1) the buffered regular system is simple and allows the increment and decrement of the least-significant digit in constant time, and (2) the strictly regular system allows the increment and decrement of a digit at arbitrary position with a constant number of digit changes while using three symbols only (instead of four symbols required by the extended regular system). To demonstrate the usefulness of the regular systems, we survey how they have been used in the design of data structures.

A reversible Turing machine (RTM) is a standard model of reversible computing that reflects physical reversibility. So far, to describe an RTM the quadruple formulation and the quintuple formulation have been used. In this paper, we propose the program form as a new formulation for RTMs. There, an RTM is described by a sequence of only five kinds of instructions. It is shown that any RTM in the quintuple form is converted to an RTM in the program form, and vice versa. We also show each instruction is implemented by a particular reversible logic element with memory called a rotary element (RE) very simply. Hence, a circuit that simulates a given RTM is easily and systematically constructed out of REs.

In cellular automata with multiple speeds for each cell i there is a positive integer (p_i) such that this cell updates its state still periodically but only at times which are a multiple of (p_i). Additionally there is a finite upper bound on all (p_i). Manzoni and Umeo have described an algorithm for these (one-dimensional) cellular automata which solves the Firing Squad Synchronization Problem. This algorithm needs linear time (in the number of cells to be synchronized) but for many problem instances it is slower than the optimum time by some positive constant factor. In the present paper we derive lower bounds on possible synchronization times and describe an algorithm which is never slower and in some cases faster than the one by Manzoni and Umeo and which is close to a lower bound (up to a constant summand) in more cases.

Partial derivatives are widely used to convert regular expressions to nondeterministic automata. For the word membership problem, it is not strictly necessary to build an automaton. In this paper, we study the size of partial derivatives on the average case. For expressions in strong star normal form, we show that on average and asymptotically the largest partial derivative is at most half the size of the expression. The results are obtained in the framework of analytic combinatorics considering generating functions of parametrised combinatorial classes defined implicitly by algebraic curves. Our average case estimates suggest that a detailed word membership algorithm based directly on partial derivatives should be analysed both theoretically and experimentally.

We study the concept of reversibility in connection with parallel communicating systems of finite automata (PCFA in short). We define the notion of reversibility in the case of PCFA (also covering the non-deterministic case) and discuss the relationship of the reversibility of the systems and the reversibility of its components. We show that a system can be reversible with non-reversible components, and the other way around, the reversibility of the components does not necessarily imply the reversibility of the system as a whole. We also investigate the computational power of deterministic centralized reversible PCFA. We show that these very simple types of PCFA (returning or non-returning) can recognize regular languages which cannot be accepted by reversible (deterministic) finite automata, and that they can even accept languages that are not context-free. We also separate the deterministic and non-deterministic variants in the case of systems with non-returning communication. We show that there are languages accepted by non-deterministic centralized PCFA, which cannot be recognized by any deterministic variant of the same type.

For a regular language L, let ({{,mathrm{Var},}}(L)) be the minimal number of nonterminals necessary to generate L by right linear grammars. Moreover, for natural numbers (k_1,k_2,ldots ,k_n) and an n-ary regularity preserving operation f, let (g_f^{{{,mathrm{Var},}}}(k_1,k_2,ldots ,k_n)) be the set of all numbers k such that there are regular languages (L_1,L_2,ldots , L_n) such that ({{,mathrm{Var},}}(L_i)=k_i) for (1le ile n) and ({{,mathrm{Var},}}(f(L_1,L_2,ldots , L_n))=k). We completely determine the sets (g_f^{{{,mathrm{Var},}}}) for the operations reversal, Kleene-closures (+) and (*), and union; and we give partial results for product and intersection.

There are two types of stateless deterministic ordered restarting automata that both characterize the class of regular languages: the stl-det-ORWW-automaton and the stl-det-ORRWW-automaton. For the former a notion of reversibility has been introduced and studied that is very much tuned to the way in which restarting automata work. Here we suggest another, more classical, notion of reversibility for stl-det-ORRWW-automata, and we show that each regular language is accepted by such a reversible stl-det-ORRWW-automaton. We study the descriptional complexity of these automata, showing that they are exponentially more succinct than nondeterministic finite-state acceptors. We also look at the case of unary input alphabets.