Definition
A hierarchy is a structure specifying the containment relationships of a number of values (or nodes or elements). A hierarchy has a single root (or top or ALL) value. A value in a hierarchy may be linked to one or more children and a non-top value is linked to one or more parents. The links between values thus specify the containment structure. Hierarchies are essential for specifying dimensions in multidimensional cubes.
Key Points
The notion of a dimension is an essential and distinguishing concept for multidimensional cubes. Dimensions are used for two purposes: the selection of data and the groupingof data at a desired level of detail. As an example, a three-dimensional cube for capturing product sales may have a Product dimension, a Time dimension, and a Store dimension. The Product dimension captures information about the product sold, such as textual description, color, weight, etc., as well as groupings of products (product groups, product families, departments,...
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Recommended Reading
Jensen CS, Pedersen TB, Thomsen C. Multidimensional databases and data warehousing, Synthesis Lectures on Data Management. San Rafael: Morgan Claypool; 2010.
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Pedersen TB, Jensen CS, Dyreson CE. A foundation for capturing and querying complex multidimensional data. Inf Syst. 2001;26(5):383–423.
Pedersen TB. Managing complex multidimensional data. In: Aufaure M-A, Zimányi E, editors. Business intelligence – second European Summer School, eBISS 2012, Brussels, Belgium, July 15–21, 2012, Tutorial Lectures, LNBIB. Brussels: Springer; 2013.
Vaisman A, Zimányi E. Data warehouse systems – design and implementation. Berlin: Springer; 2014.
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Pedersen, T.B. (2018). Hierarchy. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_887
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