Generalized Stream X- machines and Cooperating Distributed Grammar Systems

Stream X-machines are a general and powerful computational model. By coupling the control structure of a stream X-machine with a set of formal grammars a new machine called generalized stream X-machine with underlying distributed grammars, acting as a translator, is obtained. By introducing this new mechanism a hierarchy of computational models is provided. If the grammars are of a particular class, say regular or context-free, then nite sets are translated into nite sets, when k; = k derivation strategies are used, and regular or context-free sets, respectively, are obtained for k; and terminal derivation strategies. In both cases, regular or context-free grammars, the regular sets are translated into non context-free languages. Moreover, any language accepted by a Turing machine may be written as a translation of a regular set performed by a generalized stream X-machine with underlying distributed grammars based on context-free rules, under = k derivation strategy. On the other hand the languages generated by some classes of cooperating distributed grammar systems may be obtained as images of regular sets through some X-machines with underlying distributed grammars. Other relations of the families of languages computed by generalized stream X-machines with the families of languages generated by cooperating distributed grammar systems are established. At the end, an example dealing with the speciication of a scanner system illustrates the use of the introduced mechanism as a formal speciication model.