Book review Essbase & Oracle OLAP The guide to Multidimensional Analysis

Question

I won't waste the space here to talk about the book, I'll just tell you it is worth the money for it. For my full review go to
http://glennschwartzbergs-essbase-blog.blogspot.com/2010/01/book-review-oracle-essbase-oracle-olap.html

Answer 1

Prashant, DW environments are generally organized into multiple areas, some of which you've identified:
1. Source systems which provide data for the data warehouse
2. The "data warehouse" itself - a central repository for all the transactions, etc. collected from the source systems. Main function is to STORE all of the data in a clean, consistent manner
3. Possibly multiple datamarts that organize the base DW data into specific subsets that are meaningful to the end users. Can be ROLAP, MOLAP, HOLAP, etc.
Each of these tiers has different goals, which usually means they need separate architectures and/or hardware:
1. Don't put BI systems on top of your OLTP system...if a user writes a run-away query, it can bring down your transaction processing systems.....
2. DW can either be in 3nf or dimensional form, but its main job is to capture the low level transactions and make sure they conform to standards (including data quality, etc.) Users SOMETIMES run queries directly against DW tables, but once the DW starts getting big (i.e. terabytes) you probably don't want users hitting directly against it
3. OLAP datamarts are almost always in dimensional form, but only contain subsets of data from the DW. These are designed to hit very specific business problems, and typically are at a much higher level of detail than the DW.
Hope this helps. DON'T PUT YOUR DW or BI cubes on the OLTP system!!!
Scott