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    <p>Interesting question @Argnist!</p> <p>So to create some common language for my example, you want a </p> <ul> <li>DimPerson (PK=kcPerson, suggorate key for unique Persons=kPerson, type 2 dim)</li> <li>DimDocument (PK=kcDocument, suggorate key for unique Documents=kDocument, type 2 dim)</li> <li>DimAddress (PK=kcAddress, suggorate key for unique Addresses=kAddress, type 2 dim)</li> </ul> <p>A colleague has written a short blog on the usage of two surrogate keys to explain the above dims '<a href="http://www.consolidata.co.uk/SQL-blog/2008/07/using-2-surrogate-keys-on-dime.html" rel="nofollow">Using Two Surrogate Keys on Dimensions</a>'.</p> <p>I would always add DimDate with PK in the form yyyymmdd to any data warehouse with extra attribute columns.</p> <p>Then you would have your fact table as </p> <ul> <li>FactHistory (FKs=kcPerson, kPerson, kcDocument, kDocument, kcPerson, kPerson, kDate) plus any aditional measures.</li> </ul> <p>Then joining on the "kc"s you can show the current Person/Document/Address dimension information. If you joined on the "k"s you can show the historic Person/Document/Address dimension information.</p> <p>The downside of this is that this fact table needs one row for each person/document/address/date combination. But it really is a very narrow table, since the table just has a number of foreign keys.</p> <p>The advantage of this is it is very easy to query for the sorts of questions you were asking.</p> <p>Alternatively, you could have your fact table as </p> <ul> <li>FactHistory (FKs=kcPerson, kPerson, kcDocument, kDocument, kcPerson, kPerson, kDateFrom, kDateTo) plus any aditional measures.</li> </ul> <p>This is obviously much more compact, but the querying becomes more complex. You could also put a view over the Fact table to make it easier to query!</p> <p>The choice of solution depends on the frequency of change of the data. I suspect that it will not be changing that quickly, so teh alternate design of the fact table may be better.</p> <p>Hope that helps.</p>
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    1. POHow to create history fact table?
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    1. CO@Marcus D Thank you. I thought similar but without "k"s keys in fact table (Did I understand your names right? kcPerson - surrogate key for indentifying a row, and kPerson - natural key for identifying one person?).
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    2. COBut FactHistory (FKs=kcPerson, kPerson, kcDocument, kDocument, kcAddress, kAddress, kDateFrom, kDateTo) yields that we have to update old facts' kDateTo - this is not good I thought. May be better to have one kDateFrom... And one question more. Type 2 scd in DimDocument or DimAddress - for set of documents/addresses of one Person or what?
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    3. CO@Argnist. we would use two integer surrogate keys kcPerson and kPerson. kperson would be a surrogate key that points to the unique individual (regardless of name changes/gender changes etc), kcperson would be a surrogate key that points to the specific instance of that person (their specific name/gender etc). Have a check of the link I included. We dont keep natural keys on fact tables. always surrogate keys - much faster, also gets around the problem when your business users wants to change the natural key name, but retain a link to the history (yes we have had it happen!!)
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