Basic Notions

Abstract

This chapter presents the basic notions regarding multidimensional (aggregate) databases by referring to different definitions given for them in the literature. It illustrates the important concepts of micro, macro, and metadata; presents a formal definition of the aggregation process, discussing the concepts of dimension and dimension hierarchies; describes the multidimensional aggregate data structure, distinguishing between simple, complex, and composite structure; illustrates the different types of null values; and discusses differences and similarities which exist between multidimensional aggregate data (generally called statistical data because they are used mainly by statisticians) and the On-Line-Analytic Processing (OLAP) of multidimensional data represented by different data cubes, also discussing the different (symmetric and non-symmetric) treatment of dimensions and measures required by OLAP and aggregate multidimensional databases. Finally it discusses a graph model and a tabular model for this kind of data, and gives a set of definitions regarding the OLAP terminology.