Universal Guides And Finiteness And Symmetry Of Grammar Processing Algorithms

This paper presents a novel technique called "universal guides" which explores inherent properties of logic grammars (changing variable binding status) in order to characterize tbrmal criteria for termination in a derivation process. The notion of universal guides also offers a new framework in which both parsing and generation can be viewed merely as two different instances of the same generic process: guide consumption. This technique generalizes and exemplifies a new and original use of an existing concept of "proper guides" recently proposed in literature for controlling top-down left-to-right (TDLR) execution in logic progrmns. We show that universal guides are independent of a particular grammar evaluation strategy. Also, unlike proper guides they can be specified in the same mmmer for any given algorithm without knowing in advance whether the algorithm is a parsing or a generation algorithm. Their introduction into a grammar prevents as well the occurrence of certain grammar rules an infinite number of times dnring a derivation process.