Importance evaluation is one of the most challenging problems in the field of text processing. In the paper we focus on the notion of importance from a computational standpoint, and we propose a procedural, rule-based approach to importance evaluation. This novel approach is supported by a prototype experimental system, called importance evaluator, that can deal with descriptive texts taken from computer science literature on operating systems. The evaluator relies on a set of importance rules that are used to assign importance values to the different parts of a text and to resolve or explain conflicting evaluations. The system utilizes world knowledge on the subject domain contained in an encyclopedia and takes into account a goal assigned by the user for specifying the pragmatic aspects of the understanding activity. The paper describes the role of the evaluator in the frame of a larger system for text summarization (SUSY); it illustrates its overall mode of operation, and discusses some meaningful examples.
