A user interface is described which allows a user to enter input data representing a phrase, sentence, or passage of a natural language in order to cause the initiation of an action by a computer. The input data is parsed in order to generate meaning data in the form of lexical meaning representations and link data which defines the modification relationship between the lexical meaning representations. The meaning data of the input data is compared with similar meaning data for reference data by identifying a head lexical meaning representation which does not modify any other lexical meaning representations. An equivalent lexical meaning representation is identified in the reference data and then equivalent chain linked pairs of lexical meaning representations are identified in the input meaning data and the reference meaning data. The computer responds in dependence upon the degree of equivalence determined. <IMAGE>
Apparatus and method for processing natural language