Re: bitmap index and star transformation must be single colum?

  • From: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
  • To: ax.mount@xxxxxxxxx
  • Date: Thu, 7 Oct 2010 07:44:15 -0700

I dont think your schema design will work for star transformation.  I
believe the requirement is:
- primary key on column of dimension table
- bitmap index on SK column on fact table

In both cases its single column keys.  Given you cant have 2 single column
primary keys on your dimension table, it would seem it would not work.

In good design there is a single column PK and SK on the dimension and fact
table.

On Thu, Oct 7, 2010 at 12:25 AM, amonte <ax.mount@xxxxxxxxx> wrote:

> Hi
>
> I am reading 11.1 and 11.2 Data Warehousing Guide and where it explains
> about using star transformation with bitmap index in both release it states:
>
> *A prerequisite of the star transformation is that there be a
> single-column bitmap index on every join column of the fact table. These
> join columns include all foreign key columns.*
>
> Is it saying that bitmap index cannot be composite?
>
> So for example if fact table has FK against dimension such as
>
> fact.c1 ----> dim1.c1
> fact.c2 ----> dim1.c2
>
> We cannot create a bitmap index on fact.c1 and fact.c2? But we can create
> two seperate bitmap index each for each fact table column?
>
>
> Alex
>
>


-- 
Regards,
Greg Rahn
http://structureddata.org

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