MSAS: Defining Cube Properties Page - 3

Enabling write-back for a cube

Aggregation values of a cube cannot be changed without making the cube internally inconsistent. Values can be written only to the lowest levels of a cube.   Incremental change values are written either to the client cache in the PivotTable service or to a special write back table in the relational database by Analysis services.  Then, the write back values are dynamically combined with any values in the fact table for the end user.

To write back values to a cube, the client application must have write back capabilities.  The browsers in Analysis services and in Microsoft Office 2000 do not have write back capabilities.

Values can be written back to a cube permanently or temporarily.  To write back values temporarily during a what-if analysis users may use macros with the PivotTable service.  Such written back values will not be visible to other users of the cube and hence will be private. To make the write back visible to other users, the cube must be write enabled.

Write-enabling a cube means to specify a location of a relational table where the write back values will be stored.  It may be noted that the user need not write the data back to the same data source as the one containing the fact table.  Because the write-back values are stored in a relational table the tools of the relational database system can be used to append the values to original fact table.  Then the cube can be processed in Analysis Manager and the write-back data can be deleted.  We will be learning more about write back in “Actions, Drillthrough and Writeback” lesson.

Dynamically adding members to a Dimension

The Dimension browser in the Analysis Manager allows the user to add values to a dimension.  Unlike writing back values to a cube—where values are stored in a relational table—the new member in the Dimension table is added directly to the original dimension table.  The only condition being that the user must have write permissions.  This ability to dynamically add members is useful in planning applications.  The advantage is that the cube need not even be reprocessed before the new member can be used for analysis.

Removing Dimensions and measures from a cube:

This is a feature that is associated with the virtual cube in Analysis services.  The virtual cube is like the view of the relational database system.  It is restrictive and is intended to be used like a view in a sense.  However, unlike a view, whole dimensions and measures will have to be excluded if the view of data is to be restricted.  It is not possible to partially limit the view of a dimension.  The advantage is that the virtual cube can be used to combine data from more than one cube.  Calculated members can be imported from source cube into a virtual cube when the members used by the calculated member are contained in the cube.  A virtual cube can be created using the Virtual cube editor.  We will learn more about this in the lesson “Working with Virtual cubes”. 

Using the Disabled Property 

The disabled property is really the property of a level, but it only exists only within the cube editor.  The purpose of the property is to enable the user disable a level from the dimension of a cube whenever he does not require the data in the level.   The dimensions of the cube may be shared by other cubes, but the disable property disables the levels only for the cube in hand and not for the other cubes which share the data.  For instance if a user does not want to have the lower levels of a product table and only needs the Quarters of a year in the time dimension he can disable the other levels and use only the top levels of the two tables for data analysis.   The other levels will be available for other cubes that share the dimension.  To disable a level in the dimension, the user should expand the dimension, select the level and set the disabled property to “Yes”

The cube has to then be processed for the disabled property to take effect.

In this lesson we have looked at cubes, measures and properties of cubes and measures and also learnt how to work with cubes, measures and the properties of cubes.  In the next lesson we shall look at “Managing Storage and Optimization”