SET DIFFERENCE : The result of this operation, denoted by R – S, is a relation that includes all tuples that are in S but not in R .

INTERSECTION: The result of this operation, denoted by R ∩ S, is a relation that includes all tuples that are in both R and S.

The MINUS operation is commutative

UNION and INTERSECTION are commutative operations

The CARTESIAN PRODUCT operation—also known as CROSS PRODUCT or CROSS JOIN—which is denoted by ×

For the Cartesian product to be defined, the two relations involved must have disjoint headers—that is, they must have a common attribute name.

is used to combine related tuples from two relations into single “longer” tuples

The JOIN operation can be specified as aCARTESIAN PRODUCT operation followed by a PROJECT operation

A general join condition is of the form <condition> AND <condition> AND...AND <condition>

The general form is R÷ S to apply this operation the relation S must not be subset of Relation R.

An intuitive property of the division operator of the relational algebra is simply that it is the inverse of the Cartesian product.

There are two levels at which we can discuss the goodness of relation schemas

The first is the implementation (or conceptual) level

The second is the physical storage level

How users interpret the relation schemas and the meaning of their attributes.

One goal of schema design is to maximize the storage space used by the base relations

Grouping attributes into relation schemas has a significant effect on storage space.

When information is stored redundantly, this will lead to: save storage space

Cause problems with update anomalies that can be classified into