On-Line Analytical Processing (OLAP) Databases are based around the concept of amalgamating data together to make retrieving it more efficient. Replication of the same data is ok in an OLAP system. Also, the database tends to be write-restrictive. This means that data is written to it very infrequently, usually on daily, weekly, monthly, or yearly intervals. Normalization, the way On-Line Transaction Processing (OLTP) Tables are optimized, is thrown out the window. Data is grouped by dimension and fact tables. Dimension Tables usually hold the structures on how data relates. Fact Tables hold the core data. (I.E. sales per month) The tables might be detailed or contain summarized data.