Oracle-L: Re: data warehousing desing - to denormalize or not to denormalize -

From: paquette stephane <stephane_paquette_at_yahoo.com>
Date: Fri, 10 May 2002 13:38:52 -0800
Message-ID: <F001.0045EB1D.20020510133852@fatcity.com>

A DW stores data in a denormalised fashion, that's one point that every body knows but it is also subject oriented. It is also developped one subject at a time.

A DW is multi-subjects as a datamart is on one subject.

>From Bill Inmon

>From the data warehouse data flows to various
departments from their customized DSS usage. These departmental DSS data bases are called data marts. A data mart is a body of DSS data for a department that has an architectural foundation of a data warehouse.

The data that resides in the data warehouse is at a very granular level and the data in the data mart is at a refined level. The different data marts contain different combinations and selections of the same detailed data found at the data warehouse. In some cases data warehouse detailed data is added differently across the different data marts. Yet in other cases a data mart will structure detailed data differently from other data marts. But in every case the data warehouse provides the granular foundation for all of the data found in all of the data marts. Because of the singular data warehouse foundation that all data marts have, all of the data marts have a common heritage and are able to be reconciled at the most basic level.

lembark_at_wrkhors.com a écrit : >
>
> -- Gurelei <gurelei_at_yahoo.com> on 05/10/02 12:13:27
> -0800
>
> > Jared,
> >
> > Thanks for the answer. I must admit my ignorance
> in
> > terminology as for me data warehouse and data mart
> a
> > pretty much the same thing except for size. I
> > understand that data mart is smaller. The database
> I'm
> > referring to could probably be described as data
> mart
> > as it is going to be rather small - a gig or so
> maybe.
>
> "Data Mart" == summarized data from a Warehouse used
> to
> speed up query times. Main point to a mart is that
> by
> pre-aggregating the data the volume (and keyspace)
> are
> reduced. Mart's acutally increase total storage
> becuase
> they store the data more than once (Warehouse +
> agg'd
> into the Mart). Advantage is speed for the 90% of
> all
> queries that use agg'd data in the first place.
>
> --
> Steven Lembark 2930 W.
> Palmer
> Workhorse Computing Chicago, IL
> 60647
> +1 800
> 762 1582
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> Author:
> INET: lembark_at_wrkhors.com
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Stéphane Paquette
DBA Oracle, consultant entrepôt de données Oracle DBA, datawarehouse consultant
stephane_paquette_at_yahoo.com

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Received on Fri May 10 2002 - 16:38:52 CDT