Surrogate keys for degenerate dimensions?

[evgeninikolov]

Hi,

I have many facts in my model where we have degenerate dimensions (unit of measures code, currency code, county code etc.). In some cases I need the description of those codes (for instance country name, currency name etc.). So there is a need of kind of a look-up table(s).

So my question is - are those look-up tables seen as dimensions thus requiring to replace the codes with surrogate IDs or is it permitted still to continue using the smart keys themselves?

Regards,

Evgeni

[ngalemmo]

A dimensional model does not have 'look up tables'. They have fact tables, dimension tables, and bridge tables. Dimensions always have a surrogate primary key. Also, things like units of measure and currency have can far greater impact beyond simply providing a description.

[evgeninikolov]

Also, things like units of measure and currency have can far greater impact beyond simply providing a description.

Does it mean, that currency is definetly not a degenerate dimension?

[hang]

No, none of those attributes should be modeled as degenerate dimension in the fact table, as they are all low cardinality repeating groups in relation to fact. So simply put them in their respective dimension.

[sgudavalli]

Evgeni,

as said.. i dont thnk none of the below dimensions are degenerates. i guess the cardinality of degenerate is close to the facts...
and all the dimensions said below are the ones with low cardinality and definetly not degenerates...

the below so called lookup tables are real dimensions.. its always recommended to use surrogateid's to link your dimensions with a fact as it will boost the join performance and help your fact row to be more narrower...

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