[AccessD] Mucking around

Robert, be careful now.  You are starting to drift away...

Snowflake: This to me is a miltary policeman (RMP) so called because they
wore white hats.
True Stars: I can understand this cos my staff often say "Max you are a true
star" (costs me a fortune each time).

But, I *think* I am still with you.

So, we have a Form which captures data.  (Is this the transactional system
you mention).  The code then writes each entry into a Transaction Table
(flat file) all data written regardless of duplication in other data
entries.

The Transaction Table then forms part of the data mart.  There is no lookup
or linked tables. Everything is in the Transaction Table.

Have I got it right so far?

Max

 

-----Original Message-----
From: accessd-bounces at databaseadvisors.com
[mailto:accessd-bounces at databaseadvisors.com] On Behalf Of Robert L. Stewart
Sent: Friday, September 28, 2007 3:06 PM
To: accessd at databaseadvisors.com
Subject: Re: [AccessD] Mucking around

Max,

What you would normally have is an ETL (Extract-Transform-Load) process that
would get the data from the transactional system and load it into the
mart/warehouse. The data is usually transformed in some way. In the
dimension tables, all of the associated tables to the main dimension are
used to feed in the additional de-normalized data into the single dimension
table. If you do not do this, it is called snowflaking. And, this causes
poor performance from the mart/warehouse.

Marts/warehouses are not designed for efficient data storage. They are
designed for the most effective reporting possible. In some cases,
summarizing years of data into a few thousand records. No data entry would
ever be done to the mart/warehouse tables. They are always loaded via the
ETL processes defined as part of the overall strategy the business wants to
use for reporting.

I am also glad that I was able to explain it so that you were able to get
the concepts. It is usually difficult for "transactional" people to get the
concepts of a true star schema design. And they almost always want to build
snowflake schemas instead of true stars.

Robert

At 08:42 AM 9/28/2007, you wrote:
>Date: Fri, 28 Sep 2007 13:41:35 +0100
>From: <max.wanadoo at gmail.com>
>Subject: Re: [AccessD] Mucking around
>To: "'Access Developers discussion and problem solving'"
>         <accessd at databaseadvisors.com>
>Message-ID: <011c01c801cc$e8a717c0$8119fea9 at LTVM>
>Content-Type: text/plain;       charset="us-ascii"
>
>
>Hi Robert,
>Believe it or not,  I can actually understand it the way you described it.
>So, using your example, the sales would feed into the Fact Table and 
>Reports would be run on the Fact table and pull info from the Customer 
>Table.  Is this correct?
>Am I also correct in saying that this schema is highly inefficient in 
>terms of data storage but highly efficient in terms of speed of reports?
>
>Ta
>
>Max


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