2.7. Fourth Normal Form (4NF)
Fourth Normal Form (4NF) makes use of multivalued dependencies. The problem it solves is that the table has too many of them. For example, consider a table of departments, their projects, and the parts they stock. The MVDs in the table would be:
dept_name ->> jobs dept_name ->> parts
Assume that dept_name ‘d1’ works on jobs ‘j1’ and ‘j2’ with parts ‘p1’ and ‘p2’; that dept_name ‘d2’ works on jobs ‘j3’, ‘j4’, and ‘j5’ with parts ‘p2’ and ‘p4’; and that dept_name ‘d3’ works only on job ‘j2’ with parts ‘p5’ and ‘p6’. The table would look like this:
dept job part ================= 'd1' 'j1' 'p1' 'd1' 'j1' 'p2' 'd1' 'j2' 'p1' 'd1' 'j2' 'p2' 'd2' 'j3' 'p2' 'd2' 'j3' 'p4' 'd2' 'j4' 'p2' 'd2' 'j4' 'p4' 'd2' 'j5' 'p2' 'd2' ...
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