SQL Server General Quiz 2012 - Reporting and analytics cannot be achieved without a very good data model at the background

Reporting and analytics cannot be achieved without a very good data model at the background. And using Analysis services for reporting requirement is always something very common architecture. But getting data from relational engine and keeping data for analysis upto date is the challenge. What is the concept of Slowly Changing Dimension? And what is a Hybrid Slowly Changing Dimension.