Abstract. Regular expressions and the associated regular algebra provide a rich formalism for specifying and analysing sequential models of computation. For parallel computation, extensions to handle twodimensional patterns are often required. In this paper we present a new type of regular expressions for two-dimensional patterns based on contours and their composition. Targeted applications comes from the area of modelling, specification, analysis and verification of structured interactive programs via the associated scenario semantics.
Powerful algebraic techniques have been developed for classical sequential computation. Many of them are based on regular expressions and the associated regular algebra. For parallel and interactive computation, extensions to handle 2-dimensional patterns are often required. Finite interactive systems, a 2-dimensional version of finite automata, may be used to recognize 2-dimensional languages. In this paper we present a blueprint for getting a formal representation of parallel, interactive programs and of their semantics. It is based on a recently introduced approach for getting regular expressions for 2-dimensional patterns, particularly using words of arbitrary shapes and powerful control mechanisms on composition. We extend the previously defined class of expressions n2RE with new control features, progressively increasing the expressive power of the formalism up to a level where a procedure for generating the words accepted by finite interactive systems may be obtained. Targeted applications come from the area of modelling, specification, analysis and verification of structured interactive programs via the associated scenario semantics.
Two-dimensional patterns are used in many research areas in computer science, ranging from image processing to specification and verification of complex software systems (via scenarios). The contribution of this paper is twofold. First, we present the basis of a new formal representation of two-dimensional patterns based on contours and their compositions. Then, we present efficient algorithms to verify correctness of the contourrepresentation. Finally, we briefly discuss possible applications, in particular using them as a basic instrument in developing software tools for handling two dimensional words.
Two-dimensional patterns are used in many research areas in computer science, ranging from image processing to specification and verification of complex software systems (via scenarios). The contribution of this paper is twofold. First, we present the basis of a new formal representation of two-dimensional patterns based on contours and their compositions. Then, we present efficient algorithms to verify correctness of the contour-representation. Finally, we briefly discuss possible applications, in particular using them as a basic instrument in developing software tools for handling two dimensional words.
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