- Analysis Services Denali has two enginges: the traditional OLAP one (the only one it had until 2008) and the new Vertipaq one (introduced by PowerPivot and now directly available without SharePoint and/or Excel).
- In order to cover these two tecnologies under the same hat, a new acronym has been introduced: BISM (Business Intelligence Semantic Model)
- When yuo create a project for BISM you can use either BISM Multidimensional (corresponding to a classic SSAS project based on the OLAP engine) or BISM Tabular (corresponding to the new project type based on the Vertipaq engine).
- In documentation, books and article you will read Multidimensional (corresponding to BISM Multidimensional) and Tabular (corresponding to BISM Tabular).
- Both Multidimensional and Tabular models can be queried by using MDX. However, internal calculation are based on DAX in Tabular and DAX can also be used to query a Tabular model. In a possibly near future, we should expect to use DAX also to query a Multidimensional project (I hope this will happen very very soon – months and not years).
- When you install Analysis Services Denali you have to choose what type of engine you want to use for the instance you are installing. If you want to be able to use both engines, you need to install two instances of Analysis Services. During the setup you can choose which one you desire and Multidimensional is the default.
- The UDM acronym (Unified Dimensional Model) is no longer used. An UDM project is now a BISM Multidimensional project. THere is a 100% compatibility for existing projects and from the point of view of the existing feature, BISM Multidimensional is 100% corresponding to UDM in 2008 R2. Any existing book, documentation and whitepaper is still valid in BISM Multidimensional. The Analysis Services release has improvements (there is no longer a 4GB limit for string stores, for example), fix and optimizations, but there aren’t new major features in Multidimensional for this release.
– courtesy Marco Russo