Re: foundations of relational theory?

Originally posted by Mike Preece

> And 'normalisation'? You have to fit your data into a 2 dimensional

> structure although you get the sneaking suspicion sometimes that it's

> actually a lot more difficult to do so than it should be somehow?

> That's because you're insisting on making life difficult for yourself.

> Well go on if that's what rocks your boat. Knock yourself out!

>

Leaving aside the 2-dimensional fallacy, which Marshall has already addressed, what is it you imagine is so difficult about 1st normal form, which is what I think you are suggesting is difficult?

When you have an Invoice with many Invoice Lines, in Pick you create a MV item for the lines. With an RDBMS, we create a separate table for the lines. That's all. No more difficult or more easy, just different.

The beauty of the relational model is that in this example we are now equally well prepared for queries about sales of a particular product as we are for sales on a particular invoice: we have not embedded information about product sales within an MV item in an invoice; nor have we duplicated it as another MV iten within Product.

Incidentally, which would you do in Pick? Store the data once under Invoice, and then have to "un-Pick" it to get the sales by product, or store it twice?

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