7. An apparatus for analyzing the syntactic structure of a sentence used as an input to a natural language processing system, said apparatus comprising: dictionary memory means for prestoring a limited number of defined words, each of said defined words having a syntactic category; input means for receiving a sentence including a plurality of input words; dictionary consultation means connected to said input means and said dictionary memory means, for retrieving and detecting defined words respectively corresponding to the plurality of input words from among the limited number of defined words prestored in said dictionary memory means, to assign syntactic categories which are prestored with the prestored words to said input words, respectively; and means connected to said dictionary consultation means, for analyzing whether there exists at least one undefined word, other than said defined words prestored in said dictionary memory means, among the input words of said input sentence, and for assigning a syntactic category corresponding to the undefined word, independent of said dictionary consultation, when said undefined word exists in the input sentence, thereby generating a syntactic analysis result of the input sentence; wherein said means for analyzing includes; syntax analyzer means for assumptively selecting a reference syntactic category, from among a plurality of prepared reference syntactic categories, to assign said category to said undefined word included in the input sentence, said input sentence obeying a predetermined grammar rule, said grammar rule being satisfied only when the syntactic categories of the input words are arranged in a predetermined pattern and for determining whether or not a relationship between said undefined word assigned to said one reference syntactic category in the input sentence and said input words coincides with said predetermined grammar rule; said syntax analyzer means further assumptively selecting another reference syntactic category, from among the reference syntactic categories, to reapply the category to said undefined word when said another reference syntactic category applied to said undefined word has failed to coincide with the grammar rule of said input sentence in the configuration of the syntactic categories applied to said input words by said dictionary consultation.
9. The apparatus according to claim 7, wherein said syntax analyzer means sequentially repeats said grammar rule analyzing operation and said reference category reapplying operation, until the entire plurality of said reference syntactic categories are sequentially selected and completely applied to said third words, in every instance.