Syntax-Directed Translations and Quasi-alphabetic Tree Bimorphisms - Revisited
نویسندگان
چکیده
Quasi-alphabetic tree bimorphisms [Steinby and Tîrn uc : Syntax-Directed Translations and Quasi-Alphabetic Tree Bimorphisms. Proc. CIAA, LNCS 4783:265 276, 2007] are reconsidered. It is known that the class of (string) translations de ned by such bimorphisms coincides with the class of syntax-directed translations. This result is extended to a smaller class of tree bimorphisms namely (linear and complete) symbol-to-symbol tree bimorphisms. Moreover, it is shown that the class of simple syntax-directed translations coincides with the class of translations de ned by alphabetic tree bimorphisms (also known as nite-state relabelings). This proves that alphabetic tree bimorphisms are not su ciently powerful to model all syntax-directed translations. Finally, it is shown that the class of tree transformations de ned by quasi-alphabetic tree bimorphisms is closed under composition. This is known in the variable-free case and this result is extended to work with variables. Overall, the main results of [Steinby, Tîrn uc ] are strengthened.
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