 |
Home > Section 7 > Subsection 7 (Normalisation - part 1) |    |
Learning outcomes for this page:Consolidation of previous learning outcomes
Because the idea of dependency is so important I will provide another example. Consider a employee record for an SHO (Senior House Officer - a junior doctor) which has the following fields:
PIN Personal unique identifier for each employee
Full name Name of employee
Salary Salary
Contract type Full time / academic or clinical
Contract end date Date when contract ends
What can we say about the above knowing only the above facts and our knowledge of these things in the real world?
Full name is dependent upon PIN = PIN functionally determines Full name (Why? Because a PIN uniquely identifies a full name and incidentally a full name does not necessarily identify a PIN)
Salary is dependent upon PIN = PIN functionally determines Salary (Why? Because a PIN uniquely identifies a Salary and incidentally a Salary does not necessarily identify a PIN)
Contract Type is dependent upon PIN = PIN functionally determines Contract Type (Why? Because a PIN uniquely identifies a Contract Type and incidentally a Contract Type does not necessarily identify a PIN)
Contract End Date is dependent upon PIN (or possibly contract type? Only someone in the organisation will know the real answer)
PIN is not dependent upon Salary = Salary does not functionally determine PIN (Why? Because a salary does not uniquely identify a employee[=PIN])
PIN is not dependent upon Contract Type = Contract Type does not functionally determine PIN (Why? Because a Contract Type does not uniquely identify a PIN)
Looking at the 'contract type' and 'contract end date' fields the above example demonstrates once again how the process of defining the various dependencies requires those doing it to have a real understanding of the data and how it is used in their particular organisation. It is not a sterile process but related to a particular context.
For: Clinicians | NHS managers | Non healthcare workers
Draw a dependency diagram for the dependencies described above.
If you had problems understanding the above (don’t worry most people do!) create some imaginary records for the table and then draw a mapping diagram similar to the one I did earlier for the shipments example.
Written by Robin Beaumont & Chris Noden e-mail:robin@ieg-net.co.uk or chrisnoden@hotmail.com