A non-left-to-right,non-directional parser for ambiguous lattices

In syntactic pattern recognition the need of reducing computational power may require the use of more general parsers than the standard ones, allowing to efficiently exploit the structural knowledge for limiting the extraction of primitive patterns. In this paper a new flexible, non-directional, non-left-to-right parsing scheme is presented; it has worst case space complexity O(N²) and time complexity O(N³), where N is the length of the input string. These upper bounds are lowered for particular classes of context-free grammars as, for instance, linear or non-ambiguous ones.