11417476
Look-Ahead on Pushdowns
Abstract The general notion of look-ahead on pushdowns is used to prove that (1) the deterministic iterated pushdown languages are closed under complementation, (2) the deterministic iterated pushdown languages are properly included in the non-deterministic iterated pushdown languages; the counter example is a very simple linear context-free language, independent of the amount of iteration, (3) LL ( k ) iterated indexed grammars can be parsed by deterministic iterated pushdown automata, and (4) it is decidable whether an iterated indexed grammar is LL ( k ). Analogous results hold for iterated pushdown automata with regular look-ahead on the input, and LL -regular iterated indexed grammars.
13469765
Decidability of the Finiteness of Ranges of Tree Transductions
Abstract The finiteness of ranges of tree transductions is shown to be decidable for TBY + , the composition closure of macro tree transductions. Furthermore, TBY + definable sets and TBY + computable relations are considered, which are obtained by viewing a tree as an expression that denotes an element of a given algebra. A sufficient condition on the considered algebra is formulated under which the finiteness problem is decidable for TBY + definable sets and for the ranges of TBY + computable relations. The obtained result applies in particular to the class of string languages that can be defined by TBY + transductions via the yield mapping. This is a large class which is proved to form a substitution-closed full AFL.
30357320
The Power to Two-Way Deterministic Checking Stack Automata
Abstract It is well known that nondeterministic two-way checking stack automata recognize NSPACE( n ). We show that deterministic two-way checking stack automata have the same power as deterministic two-way two-head finite automata. The easy proof is based on the closure under inverse deterministic two-way GSM mappings of the deterministic two-way two-head finite automaton languages.
11003400
Passes and Paths of Attributive Grammars
An attribute grammar is pure (left-to-right) multi-pass if a bounded number of left-to-right passes over the derivation tree suffice to compute all its attributes. There is no requirement, as for the usual multi-pass attribute grammars, that all occurrences of the same attribute are computed in the same pass. It is shown that the problem of determining whether an arbitrary attribute grammar is pure multipass, is of inherently exponential time complexity. For fixed k > 0, it can be decided in polynomial time whether an attribute grammar is pure k-pass. The proofs are based on a characterization of pure multi-pass attribute grammars in terms of paths through their dependency graphs. A general result on dependency paths of attribute grammars relates them to (finite-copying) top-down tree transducers. The formal power of k-pass attribute grammars increases with increasing k. Formally, multi-pass attribute grammars are less powerful than arbitrary attribute grammars.
3010463
Equality Languages and Fixed Point Languages
This paper considers equality languages and fixed-point languages of homomorphisms and deterministic gsm mappings. It provides some basic properties of these classes of languages. We introduce a new subclass of dgsm mappings, the so-called symmetric dgsm mappings. We prove that (unlike for arbitrary dgsm mappings) their fixed-point languages are regular but not effectively obtainable. This result has various consequences. In particular we strengthen a result from Ehrenfeucht, A., and Rozenberg, G. [(1978), Theor. Comp. Sci. 7, 169–184] by pointing out a class of homomorphisms which includes elementary homomorphisms but still has regular equality languages. Also we show that the result from Herman, G. T., and Walker, A. [(1976), Theor. Comp. Sci. 2, 115–130] that fixed-point languages of DIL mappings are regular, is not effective.
35737768
A Compositional Reasoning System for Executing Nonmonotonic Theories of Reasoning
In this paper a system was developed using the compositional modelling environment DESIRE (framework for DEsign and Specification of Interacting REasoning components). This environment for the development of compositional reasoning systems and multi-agent systems has been succesfully used to design various types of reasoning systems and multi-agent systems and applications in particular domains. The DESIRE sofware environment offers a graphical editor, an implementation generator and an execution environment to execute specifications automatically.
34994233
Iterated deterministic substitution
SummaryDeterministic substitution of languages means substituting the same word (from a given language) for all occurrences of a symbol. For an arbitrary family K of languages the notion of deterministic K-iteration grammar is introduced, which is essentially the iteration of a finite number of deterministic substitutions of languages from K. The families of languages generated by these grammars are investigated.
14472583
An exercise in structural congruence
Milner's structural congruence is decidable for the pi-calculus without restriction, in exponential space.
47462408
The equivalence problem for deterministic MSO tree transducers is decidable
It is decidable for deterministic MSO definable graph-to-string or graph-to-tree transducers whether they are equivalent on a context-free set of graphs.
9865419
A compositional reasoning system for executing nonmonotonic theories of reasoning
In this paper the framework DESIRE for the design of compositional reasoning systems and multi-agent systems was applied to build a generic nonmonotonic reasoning system. The outcome is a general reasoning system that can be used to model different nonmonotonic reasoning formalisms and that can be executed by a generic execution mechanism. The main advantages of using DESIRE (for example, compared to a direct implementation in a programming language such as PROLOG) are that the design is generic and has a transparent compositional structure, and the explicit declarative specification of both the static and dynamic aspects of the nonmonotonic reasoning processes, including their control. © 2003 Wiley Periodicals, Inc.