Virtual Dimensions
A virtual dimension is a logical dimension based on the columns from a physical dimension. These contents can be either:
Member properties in the physical dimension. Member properties must be created before the virtual dimension. For more information, see Member Properties.-or-
- Columns in the tables of the physical dimension.
For example, the Store Name level of the Store dimension has a member property Store Sqft that identifies the area of the store in square feet. Using the Store Sqft member property, you can create a virtual dimension named Store Size in SqFt. This virtual dimension can be added to any cube that also contains the Store dimension.
Note You can add a virtual dimension to a cube only if the dimension that supplies the member properties or columns on which the virtual dimension is based is also included in the cube.
End users can use a virtual dimension like any other dimension. If a virtual dimension is based on member properties, the virtual dimension can enable end users to analyze cube data based on the member properties. Furthermore, the depth of the virtual dimension in terms of the number of levels it has depends on the number of member properties that are used to define it.
Adding a virtual dimension to a cube does not increase the cube's size because a virtual dimension, unlike a regular or parent-child dimension, does not have aggregation data. Virtual dimensions do not affect cube processing time because they are calculated in memory when needed. However, queries that use virtual dimensions can be slower than queries that use regular or parent-child dimensions.
Microsoft® SQL Server™ 2000 Analysis Services provides the Dimension Wizard for easy creation of virtual dimensions based on member properties.
To create a virtual dimension based on member properties
In Analysis Manager, a virtual dimension is identified by the following icon.
In Dimension Editor and Cube Editor, the Virtual property of a virtual dimension is always True. Its Depends On Dimension property indicates the dimension that contains the member properties or columns on which it is based.
When a dimension's Virtual property is set to True, an (All) level is created if one does not already exist.
All virtual dimensions are also changing dimensions. That is, their Changing property is True. This value cannot be changed while the Virtual property of the dimension is set to True.
The storage mode of a virtual dimension is always multidimensional OLAP (MOLAP).