Normalization
- 1. NORMALIZATION M.SandhiyaM.SC(IT) Department of CS&IT Nadar Saraswathi College of Arts Science Theni
- 2. Normalization • Normalization is a database design technique which organizes tables in a manner that reduces redundancy and dependency of data. • It divides larger tables to smaller tables and links them using relationships. • Normalization is the process of minimizing redundancy from a relation or set of relations. Redundancy in relation may cause insertion, deletion and updation anomalies • . So, it helps to minimize the redundancy in relations. Normal forms are used to eliminate or reduce redundancy in database tables.
- 3. Type of normal Normal Form Description 1NF A relation is in 1NF if it contains an atomic value. 2NF A relation will be in 2NF if it is in 1NF and all non-key attributes are fully functional dependent on the primary key. 3NF A relation will be in 3NF if it is in 2NF and no transition dependency exists. 4NF A relation will be in 4NF if it is in Boyce Codd normal form and has no multi-valued dependency. 5NF A relation is in 5NF if it is in 4NF and not contains any join dependency and joining should be lossless.
- 6. First Normal Form • If a relation contain composite or multi-valued attribute, it violates first normal form or a relation is in first normal form if it does not contain any composite or multi-valued attribute. A relation is in first normal form if every attribute in that relation is singled valued attribute. •
- 7. First Normal Form example
- 8. First Normal Form example • Example 2 – ID Name Courses ------------------ 1 A c1, c2 2 E c3 3 M C2, c3 • In the above table Course is a multi valued attribute so it is not in 1NF. • Below Table is in 1NF as there is no multi valued attribute • ID Name Course ------------------ 1 A c1 1 A c2 2 E c3 3 M c1 3 M c2
- 9. Second Normal Form – • To be in second normal form, a relation must be in first normal form and relation must not contain any partial dependency. A relation is in 2NF iff it has No Partial Dependency, i.e., no non-prime attribute (attributes which are not part of any candidate key) is dependent on any proper subset of any candidate key of the table.
- 10. Second Normal Form example
- 11. Second Normal Form example • Partial Dependency – If proper subset of candidate key determines non-prime attribute, it is called partial dependency. • Example 1 – In relation STUDENT_COURSE given in Table 3,FD set: {COURSE_NO->COURSE_NAME} Candidate Key: {STUD_NO, COURSE_NO} In FD COURSE_NO->COURSE_NAME, COURSE_NO (proper subset of candidate key) is determining COURSE_NAME (non-prime attribute). Hence, it is partial dependency and relation is not in second normal form. To convert it to second normal form, we will decompose the relation STUDENT_COURSE (STUD_NO, COURSE_NO, COURSE_NAME) as : • STUDENT_COURSE (STUD_NO, COURSE_NO) COURSE (COURSE_NO, COURSE_NAME) Note – This decomposition will be lossless join decomposition as well as dependency preserving.
- 12. Third Normal Form • A relation is in third normal form, if there is no transitive dependency for non-prime attributes is it is in second normal form. A relation is in 3NF iff at least one of the following condition holds in every non-trivial function dependency X –> Y 1.X is a super key. 2.Y is a prime attribute (each element of Y is part of some candidate key). •
- 13. Third Normal Form Example
- 14. Third Normal Form Example • Transitive dependency – If A->B and B->C are two FDs then A->C is called transitive dependency. – Example 1 – In relation STUDENT given in Table 4,FD set: {STUD_NO -> STUD_NAME, STUD_NO -> STUD_STATE, STUD_STATE -> STUD_COUNTRY, STUD_NO -> STUD_AGE, STUD_STATE -> STUD_COUNTRY} Candidate Key: {STUD_NO} – For this relation in table 4, STUD_NO -> STUD_STATE and STUD_STATE -> STUD_COUNTRY are true. So STUD_COUNTRY is transitively dependent on STUD_NO. It violates third normal form. To convert it in third normal form, we will decompose the relation STUDENT (STUD_NO, STUD_NAME, STUD_PHONE, STUD_STATE, STUD_COUNTRY_STUD_AGE) as: STUDENT (STUD_NO, STUD_NAME, STUD_PHONE, STUD_STATE, STUD_AGE) STATE_COUNTRY (STATE, COUNTRY)
- 15. Boyce-Code Normal Form (BCNF) – • A relation R is in BCNF if R is in Third Normal Form and for every FD, LHS is super key. • A relation is in BCNF iff in every non-trivial functional dependency X –> Y, X is a super key.
- 16. Boyce-Code Normal Form (BCNF) Example • Example 1 – Find the highest normal form of a relation R(A,B,C,D,E) with FD set as {BC->D, AC->BE, B->E} Step 1. As we can see, (AC)+ ={A,C,B,E,D} but none of its subset can determine all attribute of relation, So AC will be candidate key. A or C can’t be derived from any other attribute of the relation, so there will be only 1 candidate key {AC}. Step 2. Prime attribute are those attribute which are part of candidate key {A,C} in this example and others will be non-prime {B,D,E} in this example. Step 3. The relation R is in 1st normal form as a relational DBMS does not allow multi-valued or composite attribute.
- 17. Key Points 1.BCNF is free from redundancy. 2If a relation is in BCNF, then 3NF is also also satisfied. 3. If all attributes of relation are prime attribute, then the relation is always in 3NF. 4.A relation in a Relational Database is always and at least in 1NF form. 5.Every Binary Relation ( a Relation with only 2 attributes ) is always in BCNF.