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Section 4.1: Syntactic Analysis
Section 4.2: Semantic Analysis
Section 4.3: Conceptual Dependency
Section 4.4: Expert Systems
Section 4.5: Connected Word Recognition Using Keywords

Chapter 4

Natural Language Understanding

Natural Language is the language that we use to communicate with other people, that also can be used as an interface between humans and machines. Using natural language a user should be able to ask questions and give commands to computers in a natural way. The computer needs to understand the questions and commands to answer or perform them. But what is understanding? The operational definition of understanding is when a system performs the actions that the user asks. In this definition it is assumed that the actions chosen by the computer were the right ones.

Sometimes the system does not respond to every input, it is possible that it is modifying its internal structures and until some conditions happen it performs something that is noticeable externally. "To understand something is to transform it from one representation into another, where the second representation has been chosen to correspond to a set of available actions that could be performed and where the mapping has been designed so that for each event, an appropriate action will be performed," Rich [16] explains.

The process of understanding natural language can be decomposed into a number of steps:

  1. Input Signal - Either speech or text coming from a keyboard. This input signal is transformed into basic units (words) for the next steps.
  2. Syntactic Analysis - In this step the input words are tested to find if they are grouped according to grammatical rules, meaning that they form grammatically correct sentences.
  3. Semantic Analysis - In this step the meaning of each word and sentence is assigned. This one is the most complicated of the three steps, and unless dealing with a very simple problem domain, it requires a big knowledge data base about the topic being discussed.
In this chapter we focus our attention on Syntactic and Semantic Analysis.