Release 1 (9.0.1)
Part Number A88756-01
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| Oracle9i OLAP Services Developer's Guide to the Oracle OLAP API Release 1 (9.0.1) Part Number A88756-01 |
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Understanding OLAP API Metadata, 9 of 10
An MdmMeasure represents a set of data that is organized by one or more MdmDimension objects. The structure of the data is similar to that of a multidimensional array. Like the dimensions of an array, the MdmDimension objects that organize an MdmMeasure provide the indexes for identifying individual cells.
For example, suppose you have an MdmMeasure for sales data, and the data is organized by product, time, customer, and channel (with channel representing the marketing method, such as direct or indirect.). You can think of the data as occupying a four-dimensional array with the product, time, customer and channel dimensions providing the organizational structure. The values of these four dimensions are indexes for identifying each particular cell in the array, which contains a single sales value. You must specify a value for each dimension in order to identify a value in the array. In relational terms, the MdmDimension objects constitute a compound (that is, composite) primary key for the MdmMeasure.
The values of an MdmMeasure are usually numeric, but this is not necessary.
A given MdmMeasure is based on an OLAP measure that was created by a database administrator in the OLAP management feature of Oracle Enterprise Manager. In most cases, the database administrator specified a column in a fact table to act as the basis for the OLAP measure (alternatively, the database administrator specified a mathematical calculation or a data transformation). In many but not all cases, the database administrator also specified at least one hierarchy for each of the measure's OLAP dimensions, as well as an aggregation method. OLAP Services uses all of this information to identify the number of elements in the MdmMeasure and the value of each element.
The set of elements that are in an MdmMeasure is determined by the structure of its MdmDimension objects. That is, each element of an MdmMeasure is identified by a unique combination of elements from its MdmDimension objects.
Typically, the MdmDimension objects of an MdmMeasure are union MdmHierarchy objects. That is, they have at least one hierarchical structure. It is important to remember that the elements of a union MdmHierarchy include all of the leaves and all of the nodes for all of the level MdmHierarchy objects that represent its regions. Because of this structure, the values of the elements of an MdmMeasure are of two kinds:
MdmMeasure is based, as specified in the OLAP management feature of Oracle Enterprise Manager. These values belong to MdmMeasure elements that are identified by a combination of leaf MdmHierarchy elements.
MdmMeasure elements that are identified by at least one node element from an MdmHierarchy. The method for aggregation (for example, addition) was specified by the database administrator in the OLAP management feature of Oracle Enterprise Manager.
As an example, imagine an MdmMeasure called mdmUnitCost that is dimensioned by union MdmHierarchy objects called mdmTimesDim and mdmProductsDim. Each MdmHierarchy has leaf elements (for example, 01-JAN-99 in mdmTimesDim), and each MdmHierarchy has node elements (for example, 1999-Q1 in mdmTimesDim). A unique combination of two elements, one from each MdmHierarchy, identifies each mdmUnitCost element, and every possible combination is used to specify the entire mdmUnitCost element set.
Some mdmUnitCost elements are identified by a combination of leaf elements (for example, a particular product item and a particular month). Other mdmUnitCost elements are identified by a combination of node elements (for example, a particular product group and a particular quarter). Still other mdmUnitCost elements are identified by a mixture of leaf and node elements. The values of the mdmUnitCost elements that are identified only by leaf elements come directly from the column in the database fact table (or fact table calculation). They represent the lowest level of data. However, for the elements that are identified by at least one node element, OLAP Services provides the values. These higher-level values represent aggregated, or rolled-up data.
Thus, the data represented by an MdmMeasure is a mixture of fact table data from the data store and aggregated data that OLAP Services makes available for analytical manipulation.
The table below lists some of the elements of the MdmMeasure called mdmUnitCost, which is described above. This MdmMeasure has mdmProductsDim and mdmTimesDim as its MdmDimension objects. Each of these objects is a union MdmHierarchy with regions that are level MdmHierarchy objects. For example, the level MdmHierarchy objects for mdmTimesDim are mdmTimesDimCalHier and mdmTimesDimFisHier, and the level MdmHierarchy for mdmProductsDim is mdmProductsDimHier.
Because there are so many elements in the MdmMeasure, the table shows only a few of them. For example, for mdmTimesDim, you should imagine that the ellipses (indicated by dots) cover additional days, months, quarters, and years in the mdmTimesDimCalHier region, as well as the entire mdmTimesDimFisHier region.
mdmProductsDimHier has three levels, which represent the product category (such as Boys), the product subcategory (such as Outerwear - Boys), and the individual product item (such as #23110). The table shows only one element from each level, and the ellipses cover all the rest.
Almost all the elements shown in the table are aggregated. The ones that are not aggregated are marked with an asterisk. These nonaggregated elements are the ones that are identified by the lowest level elements of both mdmProductsDim and mdmTimesDim.
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