Systems Analysis

1
Systems Analysis Design Methods

• 4th normal form

2
Fourth Normal Formno multi-valued dependencies

• Fourth normal form has to do with so-called
  multi-valued dependencies. When faced with a
  table that is in 1NF, 2NF and 3NF, but not in
  4NF, the awkwardness of the table is emediately
  apparent. It is clear that the table contains
  information about 2 separate things.
• Imagine the following situation
• A student can follow 0,1 or more subjects.
• A student can be involved in 0, 1 or more
  activities
• These two things have nothing in common. Yet, it
  is possible to construct a table that combines
  all this information and is still in normal forms
  1,2 and 3.

3
Fourth Normal Form

• Violation Example

Student_id Subject Activity
10 Music Swimming
10 Accounting Swimming
10 Music Tennis
10 Accounting Tennis
15 Math Jogging
15 Accounting Tennis
4
Fourth Normal Form

• Remarks about the violating example
• Any combination of two fields is not enough to
  identify a record. The three fields are needed to
  form a primary key (so we are definitely in 1NF,
  2NF and 3 NF)
• Yet there are apparent redundancies here E.g.
  the fact that student 100 follows the Music
  course is recorded twice. So removing one of
  these facts would require removing 2 records.

5
Fourth normal form

• Further remarks about the violating example
• Given a value of student id, there are multiple
  values of subject possible (multivalued). Also,
  given a value for studen_id, there are multiple
  possible values for activity.
• A multivalued dependency exists between columns
  A, B, and C if A is associated with multiple
  values of B and A is associated with multiple
  values of C, but B and C are unrelated.
• (In our example of course, A is student_id)

6
Fourth Normal Form

• (Obvious )Solution

Student_id Activity
10 Swimming
10 Tennis
15 Jogging
15 Tennis
Student_id Subject
10 Music
10 Accounting
15 Math
15 Accounting