The lackness of a formal account is probably one of the most evident
of the shortcomings of information retrieval: concepts like
information, information need, and relevance are neither well
understood nor formally defined. This paper sketches a cognitive
framework that permits to analyze these three central concepts of the
information retrieval scenario.

The framework consists of concepts as cognitive agents acting in the
world, knowledge states possessed by the cognitive agents, transitions
among knowledge states, and inferences. On the basis of the framework,
information is formally defined as a pair representing the difference
between two knowledge states; this definition permits to clarify the
distinction among data, knowledge, and information and to discuss the
subjectiveness of information. On this ground, the concept of
information need is examined: it is defined, it is studied in the
context of the interaction between an information retrieval system and
a user, and the well known classification in verificative, conscious
topical, and muddled needs is analyzed. On the basis of the above
definitions of information and information need, relevance is formally
defined, and some critical features of this concept are discussed.

Keywords: Information retrieval, cognitive view, theoretical
foundations, information, information need, relevance.