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Fourth Normal Form (4NF)

A relation R is in DBMS Fourth Normal Form 4NF only if a multi-valued dependency exists in R, say A u2192u2192 B. In this case, all attributes of R are functionally dependent on A.

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Fourth Normal Form (4NF)

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  1. Language | Industrial Training | Digital Marketing | Web Technology | Testing+ | Database | Networking | Mobile Application | ERP | Graphic | Big Data | Cloud Computing WELCOME TO DUCAT INDIA Fourth Normal Form (4NF) 7070905090 info@ducatindia.com

  2. Fourth Normal Form (4NF) A relation R is in DBMS Fourth Normal Form 4NF only if a multi-valued dependency exists in R, say A →→ B. In this case, all attributes of R are functionally dependent on A For a dependency P → Q, if for an individual value of P, multiple value of Q exist, then the relationship would be a multi-valued dependency. Example Consider the relation STUDENT (SID, SUBJECT, ACTIVITY) participate in attributes. Assume that students can enroll in several different subjects and several different activities. Since this is so, the only key is the combination of (SID, SUBJECT, and ACTIVITY).

  3. STUDENT Students 200 subjects in music and accounting. He/She also participates in swimming and tennis. Student 250 subject only in math and particularly in jogging. The relation student has a multivalued dependency. Multivalued dependencies generate to update anomalies.

  4. Student 200 has four rows. Each one shows one of his subjects paired with one of these activities. If the data were stored any other way, we had only two rows: one for music and swimming and one for accounting and tennis, then the implications would be misleading. It would appear that student 100 swam only when he was a music subject and played tennis only as an accounting subject. That interpretation is illogical! These subjects and activities are entirely independent of one another. So, in this relation, we store all the combinations of subjects and activities. But data redundancy is not an essential problem with multivalued dependencies. Suppose that student 200 decides to sign up for skiing, so we add the row [200, Music, Skiing]. This implies that skies as a music subject, but not as an accounting subject. To keep consistent, we must add one row for each of these subjects paired with skiing. Thus we must also add the row [100, Accounting, Skiing]. This is an update anomaly.

  5. In general, multivalued dependencies exist when there at least three attributes in a relation. At least one of them is multivalued, and the values of two attributes depend only on the other attributes. • In other words, in a relation R (A, B, C) a multivalued dependency exists if • A leads to multiple values of C and B, and • A leads to multiple values of C and • B and C are independent of the each other. As we have seen, in the example that SID leads to multiple values of subject and multiple values of activity. Subjects and Activities are autonomous of each other. These multivalued dependencies can be indicated as follows.

  6. THANK YOU 7070905090 info@ducatindia.com

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