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1NF, 2NF, and 3NF

1NF, 2NF, and 3NF. By Vishal Punjabi. Basics. Lets first review Superkey Candidate Key Primary Key. Superkey. A set of one or more attributes, which taken collectively, uniquely identifies a tuple of a relation is referred to as a the superkey of the relation schema. Example.

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1NF, 2NF, and 3NF

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  1. 1NF, 2NF, and 3NF By Vishal Punjabi

  2. Basics Lets first review • Superkey • Candidate Key • Primary Key

  3. Superkey • A set of one or more attributes, which taken collectively, uniquely identifies a tuple of a relation is referred to as a the superkey of the relation schema.

  4. Example

  5. Ten superkeys • Rx_rx# • (Rx_rx#, Rx_pat#) • (Rx_rx#, Rx_medcode) • (Rx_rx#, Rx_dosage) • (Rx_pat#, Rx_medcode) • (Rx_rx#, Rx_pat#, Rx_medcode) • (Rx_rx#, Rx_pat#, Rx_dosage) • (Rx_rx#, Rx_medcode, Rx_dosage) • (Rx_pat#, Rx_medcode, Rx_dosage) • (Rx_rx#, Rx_pat#, Rx_medcode, Rx_dosage)

  6. Candidate key • Defined as a superkey with no proper subsets that are superkeys • A candidate key has two properties: • Uniqueness • Two tuples of a relation schema cannot have identical values for the collection of attribute(s) that constitute the candidate key • Irreducibility • No proper subset of the candidate key has the uniqueness property

  7. Two candidate keys • Rx_rx# • (Rx_pat#, Rx_medcode)

  8. Primary key (vs. candidate key) • A primary key is a candidate key (an irreducible unique identifier) with one additional property • Entity integrity constraint • Specifies that the primary key of a relation schema cannot have a “missing” value (i.e., a null value), essentially assuring identification of every tuple in a relation

  9. Why Nomarlize? What are Normal Forms? • To remove data redudancy • A stepwise progression toward the goal of a fully normalized relation schema that is guaranteed to be free of data redundancies that cause modification anomalies from a functional dependency perspective

  10. First Normal Form (1NF) Definition - A scheme R is in 1NF only when the attributes comprising the schema are atomic and single-valued. Unless a schema is in 1NF it is not a “relation schema.” That is, a relation schema is, by definition, in 1NF.

  11. Second Normal Form (2NF) Definition - A relation schema R is in 2NF if every non-prime attribute in R is fully functionally dependent on the primary key of R- i.e., a non-prime attribute is not functionally dependent on a proper subset of the primary key of R.

  12. Third Normal Form (3NF) Definition - A relation schema R is in 3NF if no non-prime attribute is functionally dependent on another non-prime in R.

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