Characterization of Hierarchies and Some Operators in OLAP Environment

Recently numerous proposals for modelling and querying Multidimensional Databases (MDDB) are proposed. Among the still open problems there is a rigorous classification of the different types of hierarchies. In this paper we propose and discuss some different types of hierarchies within a single dimension of a cube. These hierarchies divide in different levels of aggregation a single dimension. Depending on them, we discuss the characterization of some OLAP operators which refer to hierarchies in order to maintain the data cube consistency. Moreover, we propose a set of operators for changing the hierarchy structure. The issues discussed provides modelling flexibility during the scheme design phase and correct data analysis.