Even if you do not have a data modeling tool, it is beneficial to use data modeling techniques, and in particular, to design in terms of a logical schema that represents the overall structure of your organization’s data. The logical schema can then be translated into a physical schema that gives an efficient implementation.
On the first design pass, ignore interrogation requirements. An accurate business data model will normally permit sensible interrogation. When the essential model is established, test it against interrogation requirements. In particular, you may wish to introduce redundancy in order to achieve faster access. Where redundancy is introduced, only one occurrence of the redundant fields should be regarded as definitive, and it should be made clear which occurrence this is. For instance, in order to provide rapid response for telephone ordering, you might provide a current outstanding credit total for a customer as a summary field, although it is theoretically possible to build the figure up from outstanding invoices and orders.
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