OLAP Using ASP.NET - Members into Hierarchies
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The facts in a dimension are called members. By design, OLAP databases group the related facts in a member into hierarchies whenever the underlying data supports that type of structure. For example, the Time dimension in the preceding figure contains the following hierarchy:
- Year
- Quarter
- Month
- Order Date
Hierarchies use traditional parent/child relationships. For instance, Quarter is a child of Year, Month is a child of Quarter, and so on. If a child contains data that your OLAP system can aggregate, its parent level contains those aggregated sums. Some systems call those aggregated sums roll-ups. Whenever you drill up or down through your data, you navigate through those hierarchies as shown in the following figure:
The following figure gives an overview on cube (the main multidimensional structure in OLAP).
The above cube shows that it has 3 dimensions (excluding measures) namely, Source, Route and Time. All the 3 dimensions have several members (underneath them) grouped into 2 or more levels together linked in the form of a hierarchy. The measure is nothing but an aggregation of a particular column from the perspective view of dimension(s). According to the above figure, it has two measures i.e., Number of packages and Last transaction.
Note: The above explanation is just a brief introduction to the overall architecture on OLAP. For further information, refer to SQL Server 2000 online documentation or MSDN.
Next: Technical Terms in OLAP >>
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