Relational-Database-Design-Purpose-&-First-Normal-Form

• Good Relational Design
  • Retrieve information easily, obtain all constraints, minimize redundancies, and have no ambiguous

Normally, The logical design is good enough because the ER diagram is carefully designed.

• Large Schema

Suppose that instead of the schemas $course=(\underset{―}{(c\mathrm{\_}name)},credits,domain,c\mathrm{\_}number)$$offer=(\underset{―}{p\mathrm{\_}code,c\mathrm{\_}name})$ we have a larger schema $cours{e}_{i}nfo=(c\mathrm{\_}name,credits,domain,c\mathrm{\_}number,p\mathrm{\_}code)$ From the example, we see redundancy occurs.

• Small Schema

Sometimes decompositions are useless. Sometimes naive decompositions create inconsistency.

Functional Dependency

For one attribute A of the schema, the other attributes it can be identified. A->B,C,D

First Normal Form 第一范式

A domain is atomic if its elements are considered to be indivisible units. A relational schema R is in first normal form if the domains of all attributes of R are atomic. Non-atomic values complicate storage and encourage redundant (repeated) storage of data. Atomicity is actually a property of how the elements of the domain are used.