Super+Types+and+Sub+Types

Super+Types+and+Sub+Types - no 1s at the ends of the...

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Super Types and Sub Types: Additional Information This document fits best between slides 99 and 100 in the Database Lectures.pptx slide show. Here are the three tables in datasheet view: Customers (super type): IndividualCustomers (sub type #1) CommercialCustomers (sub type #2) Note that each customer in the Customers table there is a matching record in either one or the other of the sub type tables, but not both.
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See the next page for important notes on creating relationships in super type/sub type situations.
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Relationships Here is the relationship diagram. (Note that I have renamed the tables from the original example in the slides to match the naming conventions that I suggested.) In addition, note that referential integrity is NOT enforced on these relationships (there are
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Unformatted text preview: no 1s at the ends of the lines). This is because Access, unlike the book, considers one-to-one relationships to be mandatory in both directions. That is, each record in one table must have a matching record in the other, and vice versa. Since this is not how super type/sub type relationships work (records in the Customers table are only matched in one of the sub type tables, not both), we must show these relationships without referential integrity enforced. If you have super type/sub type relationships in your assignment 1 databases, you do not need to enforce referential integrity on them. You should still enforce referential integrity on all other relationships....
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This note was uploaded on 03/17/2010 for the course IOE 373 taught by Professor Snadwich during the Winter '08 term at University of Michigan.

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Super+Types+and+Sub+Types - no 1s at the ends of the...

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