Re: foundations of relational theory?

Originally posted by Mike Preece

> > > Pick file layout description:

> > > File: INVOICES

> > > ID: Invoice Number

> > > 001: Product codes (multivalued)

> > > 002: Quantity ordered (multivalued)

> > > 003: Requested Ship-by Dates (multivalued)

> > > 004: Quantity despatched - for each partial shipment
> (subvalued)

> > > 005: Despatched Date for each partial shipment
> (subvalued)

> > >

>

> <big snip>

>

> In the Pick database as described, there is one file. No pointers to

> related data. All of the related data is in a single item.

>

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?

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