Re: Announcing the "Instant Data Warehouse" Product

On the topic of large databases that do ROLAP....Metaphor Computer Systems used to do virtually all databases using star-schema. Indeed some of the tools only worked on star schema doing rolap type applications.

I am aware of star schema databases that have up to 800 million rows in the major fact table. So these things certainly scale well. Red Brick is also making inroads to large scale star schema databases, and just a few weeks ago I head that AT&T have actually used star schema to build a DW. (Hadn't heard that before...)

One of the great features of a properly implemented star schema is the fact that the summary fact tables can be implemented as 'multi-level' summary tables. This means that you can have many levels of aggregation in the one table and the user is never aware of this. Hence there is no need to understand which tables/views to look at, it is all taken care of. When you want a new summary there are no new objects to create.

In fact, in my designs I have an aggregation control table that allows a new level of aggregation to be created simply by adding a new row to the aggregation control table. It's pretty simple. (I had one client who took 55 work days to add a new aggregation level to a database(not my design), so when I designed my next WH I added the aggregate control table.)

This means that atomic data is available for ALL transactions so one can get to the lowest level of detail. Also summaries can be defined for any level the user wishes to have. One can even go back in time and create aggregations from details and have them stored to. This provides huge performance and flexibility implications. When doing trends such as number of customers, average account balance, total accounts, total balances for a set of products over a two year period for a bank that does over 1M transactions per day the odd summary is handy.

So the customer has a choice of how many summaries to keep based purely on performance requirements and disk availability....and disk prices are still coming down....

-- 
Peter Nolan
Principal Consultant
Nolan Consultants Pty. Ltd.
http://www.ozemail.com.au/~pnolan