ByVishal

Punjabi

Lets first review Superkey Candidate Key Primary Key

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.

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)

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

Rx_rx# (Rx_pat#, Rx_medcode)

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

- 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

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.

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.

Definition- A relation schema R is in 3NF if no non-prime attribute is functionally dependent on another non-prime in R.