informal Design Guidelines for Relation Schemas
- Make sure the sematics of the attributes in clear in the schema.
- Reducing the redundant information in the tuples.
- Reducing the Null values in tuples.
- Disabling the possibility of generating spurious tuples.
X -> Y
the values of component in Y is depend on or determined by, the value of X component
X is the left side of the Functional Dependency Y is the right side of the Functional Dependency
superkey: a set of attribites can uniquely distinguish a item in a relation.
key: a minimal superkey
candidate key: if a relation schema have more than 1 key, then each key is called a candidate key.
primary key: one of the candidate key can be arbitrarily designated to be the primary key.
1NF: a dormain of an attribute mush only include atomic (simple, indivisible) value. 2NF: based on full functional dependency.
A relation schema is 2NF if every noneprime attribute A in R is fully functional dependent on the primary key of R.