Re: bitmap index and star transformation must be single colum?
- From: amonte <ax.mount@xxxxxxxxx>
- To: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
- Date: Fri, 8 Oct 2010 00:23:16 +0200
Hi Greg
So that means that in Oracle if we want star transformation we must use
surrogate keys for all dimensions and fact tables FK?
Alex
2010/10/7 Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
> 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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