A Qualitative Model for Time Granularity

This paper addresses the problem of granularity in temporal representation in the context of text analysis. In contrast with other fields where granularity levels are essentially quantitative, in natural language the different levels are not always precisely defined and granularity is of a more subtle and qualitative nature. A model is proposed for representing such phenomena, based on time units and time units intervals. Time units represent chunks of time which are considered indivisible at a given granularity level, but which may be refined and contain other time units or intervals at a higher granularity level. The structure of the set of time units and intervals is studied and a relation algebra is defined which extends the traditional Allen's Point or Interval Algebra. Weak and strong representations of this algebra are proposed. We claim that such representations, called grained temporal structures, are adequate for coping with dynamic qualitative changes of granularity. A logic with restricted quantifiers is proposed for formalizing temporal knowledge and examples are discussed which show the relevance of the model for natural language analysis.