Partial Dependency
Learning outcomes for this page: Be able to describe and recognise Partial dependency
A field can be dependent upon more than one field. Consider the following which is a record detailing the procedures a number of surgeons are competent to perform along with how long, on average, it takes them to carry out each procedure. Incidentally the average value for each procedure would be obtained from some other table but we do not need to concern ourselves with this at the moment.
The composite key is shaded. This allows only one record for each procedure for each surgeon but each surgeon can perform the same procedure.
Considering the dependencies:
Average hours taken to perform a particular procedure is dependent upon both the surgeons PIN and the procedure ID. That is knowing the surgeons ID and the procedure ID determines the value for the average hours worked.
Surgeons name and Procedure name are said to be partially (functionally) dependent upon the key, while average hours is considered to be 'fully (functionally) dependent' upon the key
Elmasri & Navathe 1995 p376 provide more details concerning partial functional dependency.
Portfolio exercise: none m10|04|00
Time: 0 minutes
For: Clinicians | NHS managers | Non healthcare workers
Written by Robin Beaumont & Chris Noden e-mail:robin@ieg-net.co.uk or chrisnoden@hotmail.com
