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.
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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