tailieunhanh - Báo cáo khoa học: "Graph-structured Stack and Natural Language Parsing"

A general device for handling nondeterminism in stack operations is described. The device, called a Graph-structured Stack, can eliminate duplication of operations throughout the nondeterministic processes. This paper then applies the graph-structured stack to various natural language parsing methods, including ATN, LR parsing, categodal grammar and principlebased parsing. The relationship between the graphstructured stack and a chart in chart parsing is also discussed. | Graph-Structured stack and Natural Language Parsing Masaru Tomlta Center for Machine Translation and Computer Science Department Carnegie-Mellon University Pittsburgh PA 15213 Abstract A general device for handling nondeterminism in stack operations is described. The device called a Graph-structured stack can eliminate duplication of operations throughout the nondeterministic processes. This paper then applies the graph-structured stack to various natural language parsing methods including ATN LR parsing categorial grammar arid principlebased parsing. The relationship between the graph-structured stack and a chart in chart parsing Is also discussed. 1. Introduction A stack plays an important role In natural language parsing. It is the stack which gives a parser context-free rather than regular power by permitting recursions. Most parsing systems make explicit use of the stack. Augmented Transition Network ATN 10 employs a stack for keeping track of return addresses when It visits a sub-network. Shift-reduce parsing uses a stack as a primary device sentences are parsed only by pushing an element onto the stack or by reducing the stack in accordance with grammatical rules. Implementation of principle-based parsing 9 1 4 and categorial grammar 2 also often requires a stack for storing partial parses already built Those parsing systems usually introduce backtracking or pseudo parallelism to handle nondeterminism taking exponential time in the worst case. This paper describes a general device a graph-structured stack. The graph-structured stack was originally introduced in Tomita s generalized LR parsing algorithm 7 8 . This paper applies the graph-structured stack to various other parsing methods. Using the graph-structured stack a system is guaranteed not to replicate the same work and can run In polynomial time. This is true for all of the parsing systems mentioned above ATN shlft-reduce parsing principle-based parsing and perhaps any other parsing systems which .