DBMS:- First normal to fifth normal form
- 1. 1 Database Management System Department of Computer Science and Engineering Chitkara University, Punjab
- 2. 2 First Normal Form (1NF) • A relation or table can only be considered in 1NF if it contains only single atomic values. • 1NF disallows having a set of values, a tuple of values, or a combination of both as an attribute value for a single tuple. • In other words, 1NF disallows relations within relations or relations as attribute values within tuples. • The only attribute values permitted by 1NF are single atomic values.
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- 4. 4 Second Normal Form • Second normal form (2NF) is based on the concept of full functional dependency. • A functional dependency X → Y is a full functional dependency if removal of any attribute A from X means that the dependency does not hold anymore; that is, for any attribute A ε X, (X − {A}) does not functionally determine Y. • A functional dependency X → Y is a partial dependency if some attribute A ε X can be removed from X and the dependency still holds; that is, for some A ε X, (X − {A}) → Y. • A relation schema R is in 2NF if every nonprime attribute A in R is fully functionally dependent on the primary key of R.
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- 6. 6 Third Normal Form • Third normal form (3NF) is based on the concept of transitive dependency. • A functional dependency X → Y in a relation schema R is a transitive dependency if there exists a set of attributes Z in R that is neither a candidate key nor a subset of any key of R, and both X → Z and Z → Y hold. • A relation schema R is in 3NF if it satisfies 2NF and no nonprime attribute of R is transitively dependent on the primary key.
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- 8. 8 Boyce Codd Normal Form (BCNF) • Boyce-Codd normal form (BCNF) was proposed as a simpler form of 3NF, but it was found to be stricter than 3NF. • That is, every relation in BCNF is also in 3NF; however, a relation in 3NF is not necessarily in BCNF. • A relation schema R is in BCNF if whenever a nontrivial functional dependency X → A holds in R, then X is a superkey of R.
- 9. 9 • Example schema that is not in BCNF: in_dep (ID, name, salary, dept_name, building, budget ) because : – dept_name building, budget (holds on in_dep) but dept_name is not a superkey • When decompose in_dept into instructor and department – instructor is in BCNF – department is in BCNF
- 10. 10 (a) LOTS1A is in 3NF but not in BCNF (b) it is in 3NF, but not in BCNF due to the f.d. C B. →
- 11. 11 Fourth Normal Form • A relation schema R is in 4NF with respect to a set D of functional and multi-valued dependencies if for all multi-valued dependencies in D+ of the form , where R and R, at least one of the following hold: – is trivial (i.e., or = R) – is a superkey for schema R • If a relation is in 4NF it is in BCNF
- 12. 12 (a) The EMP relation with two MVDs: Ename –>> Pname and Ename –>> Dname. (b) Decomposing the EMP relation into two 4NF relations EMP_PROJECTS and EMP_DEPENDENTS.
- 13. 13 Fifth Normal Form • A relation schema R is in fifth normal form (5NF) (or Project-Join Normal Form (PJNF)) with respect to a set F of functional, multi- valued, and join dependencies if, – for every nontrivial join dependency JD(R1 , R2 , ..., Rn ) in F+ (that is, implied by F), • every Ri is a superkey of R. • Discovering join dependencies in practical databases with hundreds of relations is next to impossible. Therefore, 5NF is rarely used in practice.
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