Conceptual Data Warehouse Design
The advantages of using conceptual models for designing databases are well known. Conceptual models facilitate communication between users and designers since they do not require knowledge about specific features of the underlying implementation platform.
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Conceptual Data Warehouse Design
The advantages of using conceptual models for designing databases are well known. Conceptual models facilitate communication between users and designers since they do not require knowledge about specific features of the underlying implementation platform. Further, schemas developed using conceptual models can be mapped to various logical models, such as relational, object-relational, or object-oriented models, thus simplifying responses to changes in the technology used. Moreover, conceptual models facilitate the database maintenance and evolution, since they focus on users’ requirements; as a consequence, they provide better support for subsequent changes in the logical and physical schemas. In this chapter, we focus our study on conceptual modeling for data warehouses. In particular, we base our presentation in the MultiDim model, which can be used to represent the data requirements of data warehouse and OLAP applications. The definition of the model is given in Sect. 4.1. Since hierarchies are essential for exploiting data warehouse and OLAP systems to their full capabilities, in Sect. 4.2, we consider various kinds of hierarchies that exist in real-world situations. We classify these hierarchies, giving a graphical representation of them and emphasizing the differences between them. We also present advanced aspects of conceptual modeling in Sect. 4.3. Finally, in Sect. 4.4, we revisit the OLAP operations that we presented in Chap. 2 by addressing a set of queries to the Northwind data warehouse.
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Conceptual Modeling of Data Warehouses
As studied in Chap. 2, the conventional database design process includes the creation of database schemas at three different levels: conceptual, logical, and physical. A conceptual schema is a concise description of the users’ data requirements without taking into account implementation details. A. Vaisman and E. Zim´ anyi, Data Warehouse Systems, Data-Centric Systems and Applications, DOI 10.1007/978-3-642-54655-6 4, © Springer-Verlag Berlin Heidelberg 2014
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Conceptual Data Warehouse Design
Conventional databases are generally designed at the conceptual level using some variation of the well-known entity-relationship (ER) model, although the Unified Modeling Language (UML) is being increasingly used. Conceptual schemas can be easily translated to the relational model by applying a set of mapping rules. Within the database community, it has been acknowledged for several decades that conceptual models allow better communication between designers and users for the purpose of understanding application requirements. A conceptual schema is more stable than an implementation-oriented (logical) schema, which must be changed whenever the target platform changes. Conceptual models also provide better support for visual user interfaces; for example, ER models have been very successful with users due to their intuitiveness. However, there is no well-established and universally adopted conceptual model for multidimensional data. Due to this lack
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