Relational data model

The Relational Data Model uses the mathematical concept of a relation as the formalism for describing and representing data. The relations are represented as a table of values and have sets of rows, which represent certain facts about an entity or a relation in the real world. Each column has a header that represents the significance of the elements in that column.

Relational schemas are formally described as a k-ary relation schema R(A1, A2, , AK), which is a set A1, A2, , Ak of k attributes.

Example:
COURSE(course-no, course-name, term, instructor, room, time)

CITY-INFO(name, state, population)

Thus, a k-ary relation schema is a blueprint, a template for some k-ary relation.

A relational database schema is a set of relation schemas Ri (A1, A2, , Aki ), for 1 ≤ i ≤ m.

Example:

UNIVERSITY relational database schema :

STUDENT(student-id, student-name, major, status)

FACULTY(faculty-id, faculty-name, dpt, title, salary)

COURSE(course-no, course-name, term, instructor)

ENROLLS(student-id, course-no, term)

There can be certain constraints in the relational schema, and they can be:

• Key constraints - eg. one key can be a primary key, a candidate key, or a superkey
• Entity integrity constraints - eg. the primary key cannot have null values
• Referential constraints - eg. the outer key is a key that connects two entities, so they can be joined by that key