tailieunhanh - Báo cáo khoa học: "Syntactic Processing"

In computational linguistics, which began in the 1950's with machine translation, systems that are based mainly on the lexicon have a longer t r a d i t i o n than anything e l s e - - - f o r these purposes, twenty f i v e years must be allowed to count as a tradition. The bulk of many of the early translation systems was made up by a d i c t i o n a r y whose e n t r i e s consisted o f a r b i t. | Syntactic Processing Martin Kay Xerox Palo Alto Research Center In computational linguistics which began In the 1950 s with machine translation systems that are based mainly on the lexicon have a longer tradition than anything else for these purposes twenty five years must be allowed to count as a tradition. The bulk of many of the early translation systems was made up by a dictionary whose entries consisted of arbitrary Instructions In machine language. In the early 60 3 computational linguists at least those with theoretical pretentions abandoned this way of doing business for at least three related reasons First systems containing large amounts of unrestricted machine code fly In the face of all principles of good programming practice. The syntax of the language in which linguistic facts are stated Is so remote from their semantics that the opportunities for error are very great and no assumptions can be made about the effects on the system of Invoking the code associated with any given word. The systems became virtually unmaintainable and eventually fell under their own weight. Furthermore these fallings were magnified as soon as the attempt was made to Impose more structure on the overall system. A general backtracking scheme for example could all too easily be thrown Into complete disarray by an Instruction In a single dictionary entry that affected the control stack. Second the power of general and particularly nondetermlnlstlc algorithms In syntactic analysis came to be appreciated. If not overappreolated. Suddenly It was no longer necessary to seek local criteria on which to ensure the correctness of Individual decisions made by the program provided they were covered by more global criteria. Separation of program and linguistic data became an overriding principle and since It was most readily applied to syntactic rules these became the main focus of attention. The third and doubtless the most Important reason for the change was that syntactic theories In .