1 CSC 1035 Supplement for Chapter 2 Functional Dependencies

2 Definition and Notation Suppose X and Y are sets of attributes (column names) Check whether this statement is true or not: “For every set of values in the X columns, there can be at most one set of values in the Y columns” If that’s true, then say X determines Y And write X -> Y

3 An example of some FD’s Suppose the attribute names are: stuId, firstName, lastName, major, credits, classNumber, grade, schedule, room, facId, name, rank, department And suppose the semantics are the same as in University.mdb On the next pages, let’s analyze those attributes for FD’s.

4 Examples from University.mdb This statement is true: “For every set of values of stuId, classNumber, there can be at most one grade.” So is this one: “For every value of stuId, there can be at most one value of firstName and lastName. This one isn’t true: “For every value of classNumber, there can be at most one value of stuId.”

5 Examples, continued Phrasing the examples from the previous slide in technical database language: –stuId, classNumber -> grade –stuID -> firstName, lastName –classNumber does NOT determine stuId

6 Here’s a complete list of FD’s stuId -> firstName, lastName, major, credits stuId, classNumber -> grade classNumber -> room, schedule, facId facId -> name, rank, department

7 Setting up the tables in the database Each of the FD’s in the last slide should lead to its own table. Within each table, the left-hand part of the FD becomes the primary key. So rather than a single table with all 13 attributes, we get four tables, each with fewer attributes. The big table would have had redundancies.

8 Normalization The process of decomposing a big table into smaller ones, in order to avoid redundancies and anomalies, is called normalization. An indication of a table that’s not normalized would be if you can spot a FD X->Y where X isn’t a key for that table.