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Grammar Systems versus Membrane Computing: The Case of CD Grammar Systems

In this paper we discuss some relationships between grammar systems and P systems (membrane systems), two areas of computer science dealing with distributed computing models, but with different motivations and different types of basic ingredients. We extend one of the most important communication protocols of cooperating distributed (CD) grammar systems, the so-called t-derivation mode, to P systems with string-objects: if no rule can be applied to a string in a region of a P system, then the string is moved to a neighbouring region, depending on the communication mode either in exactly one direction (in or out) or in both directions. We describe the computational power of the obtained classes of P systems in comparison with families of languages generated by grammars in the Chomsky hierarchy or with CD grammar systems and formulate several problems for future research.