Re: Data Model - Please Comment on my Approach
Date: Sat, 24 May 2003 13:06:09 -0400
Message-ID: <t79oab.e9g.ln_at_mercury.downsfam.net>
Quoting unnamed sources, Karsten Farrell claimed:
> 71062.1056_at_compuserve.com said...
>> The rest of your design is a meta-data >> model, with column descriptions. You will wind up with monster joins. >> Sorry, but this is not a good idea at all. The original model is >> correct. >>
>
> Well, I have two comments:
>
> 1. There is nothing wrong with joins. They are a part of life in the
> RDBMS world. You normally eliminate many of them when you build a Data
> Warehouse, but ONLY then. One of the most common type of joins is done
> to "convert" (display) a code to its description (they're called lookup
> tables, for obvious reasons).
>
> 2. The original model is not even first normal form (1NF), but is
> reminiscent of the flat-file databases of the 1970s. Normally you try to
> get your model to at least 3NF. To get to 1NF, you eliminate all the
> column "arrays" - even though they're not called that in a table. The
> reason the original model is flawed becomes obvious when someone decides
> to breakdown age brackets into smaller (or larger) groups than the
> current 5-year groups ... or they want to capture other income levels
> ... or they want to toss in another house type. If you have stored
> nothing but totals, you'll have no way to determine which of the tens or
> thousands now fall into the split/joined categories.
The analysis you describe are not often done, because the type of data being collected, which is summaries of personal information, is usually heavily regulated. There is no point in considering the case of different age break downs because by law the person receiving the summary cannot receive the detail that produced it.
Marketing/Demographic databases are much like data warehouses, in that you flatten out the tables for faster access, but unlike a warehouse, you rarely if ever have access to the underlying data.
Because of all of this, you usually have an industry that expects certain categories of age groups, income brackets and so forth because that's what the big houses (experion, axciom and others) are putting out.
-- Kenneth DownsReceived on Sat May 24 2003 - 19:06:09 CEST