[AccessD] Re: Using Dates

Hi Robert

> What I think he is saying is that in 99% of the cases, the regular date
> dimension table will work.  In a few cases, where the date may be missing 
> and you want to get some kind of value for it, you cannot use the date 
> itself as the key, thus the surrogate.  The surrogate would be stored in 
> the fact tables (another data warehousing concept, for those that do not 
> know about them).  That way when you hit an invalid or null date value, the 
> date dimension table would be able to handle it in a predefined way.

I noticed this too and wondered. How can one "hit an invalid date"? Do
dataware house people not validate data before storing them? A missing
date may, of course, be accepted, but an invalid? Where would that
come from?

/gustav


>>I'm not even sure what Ralph is saying there, and it flies in the face
>>of what he does in some of his books, so I have no answer for you, John.
>>Keep in mind, though, that datawarehouses are indexed somewhat
>>differently from transactional databases, so that may be where the
>>confusion is coming in.  If you were using surrogate keys and
>>meaningless values as the PK, the dates in the main records would need
>>to be inserted *from* the date table, and that isn't generally the way
>>the thing is used.
>>
>>Charlotte Foust