File Structures
DISCUSSION III:
FUNCTIONAL DEPENDENCY & 2NF
Dr Chris Anagnostopoulos
[TASK 1] FUNCTIONAL DEPENDENCY
Which of the FDs in this relation instance might hold true?
2
[TASK 1] FUNCTIONAL DEPENDENCY
Which of the FDs in this relation instance might hold true?
Answer:
Z → Y
X → Y
{X,Z} → Y
3
[TASK 2] INFERENCE RULES
Is this true?
If {X,Y} Z then X Z and Y Z
5
[TASK 2] INFERENCE RULES
Is this true?
If {X,Y} Z then X Z and Y Z
Answer: No, XYZ means that a combination of X and Y uniquely
determines Z; not alone X or Y can determine Z.
{StudentID, CourseID} Grade
does not imply that
StudentID Grade and CourseID Grade
//It is the grade for a specific student in a specific course! 6