Parsing English Conjunctions And Comparatives Using The Wait-And-See Strategy

The major problems in parsing conjunction and comparative English sentences are ambiguities of the scoping and the ellipsis. For a correct parsing, the parser must use not only the syntax but also the semantic information of these sentences. However, as Chiang et. al. [1] pointed out, the semantic information of these sentences can only be obtained after these sentences have been parsed. It is also the reason why a syntax-directed parsing strategy without collecting adequate semantics of input sentences needs to backtrack each time when it makes incorrect assumptions during parsing. The Wait-And-See strategy, introduced by Marcus [2], is based on the 'determinism hypothesis' which claims that the natural language can be parsed by a computationally simple mechanism without backtracking. In this paper, we show a method using the Wait-And-See strategy to parse conjunctions and comparatives simultaneously. In order to enhance the efficiency and correctness of the parser, several mechanisms such as bottom-up preparsing, suspension, and pattern matching are implemented. The bottom-up preparsing looks up the dictionary and recognizes isolated sentence fragments which can be determined without ambiguities. Suspension allows the parser to suspend temporally at ambiguous points and continue to parse the rest of the sentence until it obtains necessary information to resolve the ambiguities. Pattern matching uses the concept of symmetry to detect missing components (the ellipses) in the two conjuncted or compared sentence fragments.