Metadata Management Concept for Multidimensional OLAP Data Based on Object-Oriented Concepts O. Mangisengi, A M. Tjoa Institute of Software Technology, Technical University of Vienna, Austria e-mail: {oscar,tjoa}@ifs.tuwien.ac.at R.R. Wagner Institute of Applied Knowledge Processing, University of Linz, Austria e-mail: wagner@ifs.uni-linz.ac.at Abstract This paper introduces metadata management concept based on the object-oriented paradigm for modeling and querying multidimensional OLAP-data. In this model we apply the basic concepts of the object-oriented model including object, class, and relationship between objects to describe objects of multidimensional data and the OLAP operations. In our approach the multidimensional OLAP-data is modeled as a fact and a set of dimensions that are organized into class-hierarchy. 1. Introduction On-line Analytical Processing (OLAP) is emerging as the most important approach in Data Warehousing. OLAP allows modeling data in a multidimensional way as a cube and to query and analyze data from many different perspectives. Independent from the different implementation aspects, OLAP data are presented to the user in a multidimensional data model [4]. There are several ways how to formally define multidimensional models and their query languages. However until now there do not exist a commonly accepted formal multidimensional data model. Such a model is necessary as a basis for an accepted standardized logical data model for OLAP data. This would allow practitioners and researchers to specify their data warehouses in a unified way. The aim of this paper is to propose an approach for a meta model of multidimensional data with capability to describe objects and the OLAP operations based on the object-oriented model. It seems to the authors that such a model would very much correspond with the original intuition of Codd, when he introduced the concept of OLAP in his pioneering white paper [4]. Recently a number of approaches are developed for the formal foundation of multidimensional modeling of OLAP-data, such as Blaschka, el al. in [3], compares and describes the four most important modeling approaches in this area, namely the approaches [1] of Agrawal, Gupta, and Sarawagi, ([6],[7]) of Cabbibo and Torlone, [12] of Li and Wang, and [9] of Gyssens and Lakshmanan, Mangisengi, et al. in [13], and Trujillo and Palomar in [14]. This paper intends to apply the object-oriented concept for OLAP modeling of multidimensional data. In this approach multidimensional cube class is organized into class-hierarchy, which consists of three layers and each layer has an independent function. In modelling OLAP- data within the object-oriented paradigm we would like to take advantage from the several positive aspects of object- oriented modelling, such as security, reusable software, etc. The remainder of this paper is organized as follows. Section 2 briefly presents the multidimensional data model. In section 3 we present the modeling of OLAP- data based on the object-oriented concepts. Section 4 presents an extended example for the use of object- oriented modeling in a Data Warehouse. Our conclusion is given in section 5. 2. The Multidimensional Data Model  Multidimensional OLAP data is presented as a multidimensional data cube. The multidimensional data cube can be modeled by using facts and a set of dimensions based on the notion of dimension hierarchy. 2.1. Fact and Dimensions Let { } O O /   L = be a set of level names, where each level / O ³ is associated with a set of values () O GRP ; let { } G G '   L = be as finite set of dimensions (D); and let { } I I )   L = a finite set of fact names (F).