Pushdown Automata and Context-Free Grammars in Bisimulation Semantics

Bisimulation of Context-free Grammars and of Pushdown Automata

We consider the bisimulation on the transition graphs of pushdown automata. First we give a characterization of bisimulation using the unfolded trees. We recall that the bisimulation is decidable for the subclass of preex transition graphs of context-free grammars. Furthermore any pushdown transition graph is a regular graph: it can be generated by iterated parallel rewritings of a deterministi...

Balanced Context-Free Grammars, Hedge Grammars and Pushdown Caterpillar Automata

The XML community generally takes trees and hedges as the model for XML document instances and element content. In contrast, Berstel and Boasson have discussed XML documents in the framework of extended context-free grammar, modeling XML documents as Dyck strings and schemas as balanced grammars. How can these two models be brought closer together? We examine the close relatioship between Dyck ...

Unary Context-Free Grammars and Pushdown Automata, Descriptional Complexity and Auxiliary Space Lower Bounds

It is well known that a context-free language defined over a one-letter alphabet is regular. This implies that unary context-free grammars and unary pushdown automata can be transformed into equivalent finite automata. In this paper, we study these transformations from a descriptional complexity point of view. In particular, we give optimal upper bounds for the number of states of nondeterminis...

Graph Interpolation Grammars as Context-Free Automata

A derivation step in a Graph Interpolation Grammar has the effect of scanning an input token. This feature, which aims at emulating the incrementality of the natural parser, restricts the formal power of GIGs. This contrasts with the fact that the derivation mechanism involves a context-sensitive device similar to tree adjunction in TAGs. The combined effect of input-driven derivation and restr...

Simulating finite automata with context-free grammars