Re: foundations of relational theory?

Originally posted by andrewst

> In that case, where do the Product Codes come from? Does the clerk
> just invent them as s/he types in the order?

>

> And if presumably the Invoice is to a Customer about whom we hold
> details (and perhaps many previous Invoices), do you not need a
> relationship between Invoices and Customers? Or perhaps you would
> replace the Invoices file by a Customers file where the invoices are
> embedded as a multivalued item?

I can't be sure that I recall correctly, but I think I mentioned that the Product Numbers had to exist in a Product File and that the Sizes and Colours had to be on the Product item.

I did omit to mention the Customer. Sorry. I am of course making this up as we go along.

Can we not simply assume that these other files are taken care of for the purposes of this example? If we start defining the Customer and Product files we could get into a "but what about the ... file?" situation and we'd never get anything done. If, for the purposes of implementing an SQL-relational equivalent you need this inforrmation then go ahead and invent it. Tell me what you've done and I'll try to replicate it on the Pick system if you like.

Mike.

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