HOLAP
Some vendors provide the ability to access relational databases directly from an MDDB, giving rise to the concept of hybrid OLAP environments. This implements the concept of "drill through," which automatically generates SQL to retrieve detail data records for further analysis. This gives end users the perception they are drilling past the multidimensional database into the source database.
The hybrid OLAP system combines the performance and functionality of the MDDB with the ability to access detail data, which provides greater value to some categories of users. However, these implementations are typically supported by a single vendor’s databases and are fairly complex to deploy and maintain. Additionally, they are typically somewhat restrictive in terms of their mobility.
Source: Business Insight Beyond OLAP - CorVu Corporation
http://www.corvu.com/library/whitepapers/beyondolap.html