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

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
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.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
See the next page for important notes on creating relationships in super type/sub type situations.
Background image of page 2
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
Background image of page 3
This is the end of the preview. Sign up to access the rest of the document.

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....
View Full Document

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.

Page1 / 3

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

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online