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Understanding Database Normalization: Key Concepts and Higher Normal Forms

eljah avatar
eljah
11 diapositives · 280 Views · Sep 06, 2014

This summary covers essential concepts in database normalization, a process that minimizes data redundancies. The first three normal forms (1NF, 2NF, and 3NF) are introduced, detailing the conditions for each. A table is in 1NF when all key attributes are defined, in 2NF when it is free from partial dependencies, and in 3NF when there are no transitive dependencies. The Boyce-Codd Normal Form (BCNF) is also discussed, emphasizing the importance of candidate keys. Higher normal forms, such as 4NF, are mentioned, showcasing their relevance in complex databases.

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  1. Schema Refinement and Normal FormsChapter 19

  2. Database Systems, 10th Edition Summary • Normalization minimizes data redundancies • First three normal forms (1NF, 2NF, and 3NF) are most commonly encountered • Table is in 1NF when: • All key attributes are defined • All remaining attributes are dependent on primary key

  3. Database Systems, 10th Edition Summary (cont’d.) • Table is in 2NF when it is in 1NF and contains no partial dependencies • Partial dependency • Exists when there is a functional dependence in which the determinant is only part of the primary key • Table is in 3NF when it is in 2NF and contains no transitive dependencies • Transitive dependency • Exists when there are functional dependencies such that X → Y, Y → Z, and X is the primary key • Table that is not in 3NF may be split into new tables until all of the tables meet 3NF requirements

  4. Database Systems, 10th Edition Higher-Level Normal Forms • Tables in 3NF perform suitably in business transactional databases • Higher-order normal forms are useful on occasion • Two special cases of 3NF: • Boyce-Codd normal form (BCNF) • Fourth normal form (4NF)

  5. Database Systems, 10th Edition The Boyce-Codd Normal Form • Every determinant in table is a candidate key • Has same characteristics as primary key, but for some reason, not chosen to be primary key • When table contains only one candidate key, the 3NF and the BCNF are equivalent • BCNF can be violated only when table contains more than one candidate key

  6. Database Systems, 10th Edition The Boyce-Codd Normal Form (cont’d.) • Most designers consider the BCNF as a special case of 3NF • Table is in 3NF when it is in 2NF and there are no transitive dependencies • Table can be in 3NF and fail to meet BCNF • No partial dependencies, nor does it contain transitive dependencies • A nonkey attribute is the determinant of a key attribute

  7. Database Systems, 10th Edition Normalization and Database Design (cont’d.) • ER diagram • Identify relevant entities, their attributes, and their relationships • Identify additional entities and attributes • Normalization procedures • Focus on characteristics of specific entities • Micro view of entities within ER diagram • Difficult to separate normalization process from ER modeling process

  8. Homework 2 • Posted in course webpage • Due date: 11/12 (Next Tuesday)

  9. Boyce-Codd Normal Form (BCNF) • Reln R with FDs F is in BCNF if, for all X A in • A X (called a trivial FD), or • X contains a key for R. • In other words, R is in BCNF if the only non-trivial FDs that hold over R are key constraints.

  10. Third Normal Form (3NF) • Reln R with FDs F is in 3NF if, for all X A in • A X (called a trivial FD), or • X contains a key for R, or • A is part of some key for R. • Minimality of a key is crucial in third condition above! • If R is in BCNF, obviously in 3NF. • If R is in 3NF, some redundancy is possible. It is a compromise, used when BCNF not achievable (e.g., no ``good’’ decomp, or performance considerations). • Lossless-join, dependency-preserving decomposition of R into a collection of 3NF relations always possible.