For a long time relational models have supported the ability to create virtual tables known as “views” to provide a mechanism that allows developers to customize how their users can logically view data stored in base tables.
There is a similar concept in Cognos TM1 known as “virtual cubes”. A virtual cube is a cube that contains no physical data but though TM1 rules refers to and displays data that persists within a TM1 server.
If we use a virtual cube, we are not restricted to the dimensionality of a particular cube or cubes; in fact, we can combine or dissect dimensions, perform mathematical calculations, and filter or summarize slices of data to create a view that is the most optimal to a particular user, group or reporting need.
Why not just build cubes that way in the first place? Well, in the first place, you model your cubes to support analytical analysis. This means breaking apart data into (the simplest) chunks that you need to report on – this breakout supports potentially endless “slicing and dicing” but can create extra work when building reports -as a report more realistically will want to see rows with columns showing totals that are based upon a combination of dimensions.
Cube Viewer
Virtual cubes will extend the usefulness of TM1’s Cube viewer since virtual cubes are not restricted by the dimensionality of a cube users can create views that are more conducive for general reporting and therefore eliminate (or at least reduce) the need for more “formal” reporting options such as a TM1 Web sheet or Cognos BI report.
Security
Virtual cubes can also be used to simplify security. Granting access to a particular cube is always easier to implement than element of cell security models. Virtual cubes can be the mechanism that restricts users to a certain subset of data in one or more base cubes.
Performance
Virtual cubes can also be defined to provide system performance benefits, improving data access on the most complex queries by precomputing and materializing a view of data.
Conclusion
To be sure, virtual cubes are not a slam dunk – careful consideration must go into their design and implementation – but they certainly deserve an earnest evaluation before your next TM1 implementation.
“We all live every day in virtual environments, defined by our ideas” – Michael Crichton
