Continued advances in hardware technologies combine to create a new class of information services, termed mobile e-services, or simply m-services, which exploits the advances in, among others, wireless communications, positioning, and miniaturization. Because the users do not merely interact with the services from behind stationary desktop computers, but from a variety of increasingly unobtrusive information appliances while on the move, location information plays a fundamental role, and new types of services become of interest. Such services include tracking, way-finding, traffic management, safety-related services, and mixed-reality games, to name but a few. Data warehousing has the potential for playing an essential part in m-services. However, for data warehousing to be successful in an m-service scenario, new challenges must be met by data warehousing technologies. Such challenges include support for non-standard dimension hierarchies and imprecision and varying precision in the data; transportation networks; continuous change; closed-loop usage; and dynamic services. This paper outlines a general m-services scenario and describes central challenges to be met by data warehousing in order for it to reach its full potential for usage in m-services.
Das wichtigste Einsatzgebiet von Data Warehouses ist die multidimensionale Analyse der Daten mittels OLAP-Tools. Die Dimensionen dienen dabei typischerweise der Beschreibung der Zeit, der Kennzahlen und der (betrieblichen) Strukturen wie zum Beispiel Abteilungen, Kostenstellen oder auch Kostenarten. Solche Strukturen sind jedoch dynamisch, was zu laufenden Anpassungen der multidimensionalen Sicht auf die Daten fuhrt. Wir zeigen in dieser Arbeit, wie man mit solchen Strukturanderungen umgehen kann ohne Abstriche bzgl. der Konsistenz und Aussagekraft von Analysen machen zu mussen. Dieser Ansatz basiert im wesentlichen auf der Erweiterung des bekannten Data Warehouse Konzepts um temporale Aspekte, und Transformationsfunktionen die zur Hinterlegung von Beziehungen zwischen unterschiedlichen Strukturversionen dienen.
Database systems offering a multidimensional schema on a logical level (e.g. OLAP systems) are often used in data warehouse environments. The user requirements in these dynamic application areas are subject to frequent changes. This implies frequent structural changes of the database schema. In this paper, we present a formal framework to describe evolutions of multidimensional schemas and their effects on the schema and on the instances. The framework is based on a formal conceptual description of a multidimensional schema and a corresponding schema evolution algebra. Thus, the approach is independent of the actual implementation (e.g. MOLAP or ROLAP). We also describe how the algebra enables a tool supported environment for schema evolution.
New application areas for databases like data warehousing and OLAP (Online Analytical Proc-essing) deploy the multidimensional data model in order to describe the application domain. Consequently, OLAP systems are represented by a multidimensional database schema to adequately reflect the application semantics. FIESTA presents a methodology for the evolution of such multidimensional schemas. Core of the thesis is a schema evolution algebra which comprehends a formal multidimensional data model together with corresponding schema evolution operations. Since OLAP systems are typically implemented as additional layer for relational database systems, the processing of sequences of schema evolution operations in a relational database system is presented. To this end, we formally describe how a multidimensional schema can be mapped to a corresponding relational database schema. In order to fully maintain the multidimensional semantics during this transformation, a corresponding meta schema is introduced as extension of the relational system catalogue. For a consistent processing of evolution operation sequences, a transformation to corresponding relational evolution commands is performed. These relational evolution commands adapt the relational database schema together with the instances and update the contents of the meta schema accordingly. A prototype for FIESTA has been implemented as part of a graphical design environment for data warehouses. In this environment, multidimensional schemas are presented at the user interface by means of a specialized graphical notation. This notation is an extension of the well-known Entity/Relationship approach. For internal processing the graphical representation is transformed to an algebraic description of the multidimensional schema.
