Attribute Refinement in a Multigranular Temporal Object Data Model ⋆ E. Bertino 1 E. Camossi 2 G. Guerrini 3 1 CERIAS - Purdue University, 250 N. University Street West Lafayette, Indiana, USA 47907-2066. Phone: +1 765 496-2399. Fax: +1 765 494-0739. e-mail: bertino@cs.purdue.edu 2 School of Computer Science and Informatics - University College Dublin, Belfield, Dublin 4, Ireland. Phone: +353 (0)1 7162-944. Fax: +353 (0)1 2697-262. e-mail: {elena.camossi}@ucd.ie 3 DISI - Universit`a degli Studi di Genova, Via Dodecaneso 35, 16146 Genova, Italy. Phone: +39 010 353-6701. Fax:+39 010 353-6699. e-mail: guerrini@disi.unige.it Abstract. Temporal granularities are the unit of measure for tempo- ral data, thus a multigranular temporal object model allows to store temporal data at different levels of detail, according to the needs of the application domain. In this paper we investigate how the integration of multiple temporal granularities in an object-oriented data model im- pacts on the inheritance hierarchy. In the paper we specifically address issues related to attribute refinement, and the consequences on object substitutability. This entails the development of suitable instruments for converting temporal values from a granularity to another. 1 Introduction Temporal object data models allow to maintain the values taken by object at- tributes over time. Conventional object database systems do not offer a support for dealing with time-varying objects. The content of a database represents a snapshot of the reality in that only the current values of object attributes are recorded, without the possibility of maintaining the complete history of objects over time. If such a need arises, object attribute histories must be managed at application program level. A direct support for temporal objects at database level, by contrast, would greatly simplify their management and handling. Thus, in the past years, there has been a growing interest in temporal extensions to the current database technology. Several extensions to the relational and the object-oriented data models and query languages have been proposed [15, 24]. An important requirement, when dealing with temporal aspects, concerns the support for multiple temporal granularities [7]. Temporal granularities are the ⋆ Research presented in this paper was funded by a Strategic Research Cluster grant (07/SRC/I1168) by Science Foundation Ireland under the National Development Plan. The authors gratefully acknowledge this support. The work of Elena Camossi is supported by the Irish Research Council for Science, Engineering and Technology.