Why does BW use surrogate keys ?

Hi,
can anyone answer me in 1 sentence:
Why dos BW uses surrogate / artifical keys ?
Its not faster while querying - line items are faster & y need query more tables.
Its not faster while loading - surrogate keys need to be looked up and build up.
ThanXs
Martin

A database don't care if it's numeric or not. Index access is index access and that is what matters. But talking about indexes. There is less index'es to maintain when you use surrogates, otherwise you should have an index on each characteristic in the fact table, and it could be a lot. Also there may be a historical technical reason, like the number of key fields available on a table. Remember that SAP is trying to be DB vendor independent so if a supported DB only accepts say 16 key fields, then you need to design you application for that.
-Kristian

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