Natural Language Understanding Wiki

Top-down process[]

A top-down process, also called expectation-driven process, is one that use what a person knows predict words and sentences that she would find in a text she is reading.

The process is proposed to resolve the problem of combinatoric explosion. For a short sentence of 10 words, if each word has 5 senses, the number of combinations reach the millions. It seems that in the reader mind sits a smart "driver" that always know the right way through the sentence.

From Kintsch (1988)[1]: "Parsing a sentence is often thought of as predicting each successive constituent from those already analyzed on the basis of syntactic rules (Winograd, 1983). Scripts, frames, and schemata constrain the inferences an understander makes (as in Schank & Abelson, 1977), thereby preventing the process from being swamped in a flood of irrelevancies and redundancies."

From Schank (1978, p. 94[2], as cited in Kintsch, 1988[1]): "We would claim that in natural language understanding, a simple rule is followed. Analysis proceeds in a top-down predictive manner. Understanding is expectation based. It is only when the expectations are useless or wrong that bottom-up processing begins."

The top-down approach is usually tied to hand-crafted production system in the kind of Chomskian grammar.

Bottom-up process[]


  1. 1.0 1.1 Kintsch, W. (1988). The Role of Knowledge in Discourse Comprehension - a Construction Integration Model. Psychological Review, 95(2), 163–182.
  2. Schank, R. C. (1978). Predictive understanding. In R. N. Campbell & P. T. Smith (Eds.), Recent advances in the psychology of language-- Formal and experimental approaches (pp. 91-101). New York: Plenum Press.