I. Introduction
RECENT RESEARCH in language engineering has taken natural language processing beyond the sentence level, not only because textual analysis is necessary, but also because of the difficulties of textual knowledge extraction in the enormous information cyberspace where there is constant massive dissemination of written text. Textual knowledge extraction involves interpretation of the text at a reasonable level and identification of the relative importance of each word. While the techniques involved in full text summarization are far beyond the state-of-the-art in current linguistics, the great demands in the community of information retrieval (IR) which struggle to move beyond keywords has motivated the research on the extraction of salient textual patterns and the identification of textual regularities [36], [45], [49].