THE RELATIONAL DATABASE MODEL

THE THREE WELL-DEFINED COMPONENTS OF THE RELATIONAL MODEL

1. A LOGICAL DATA STRUCTURE REPRESENTED BY RELATIONS 2. A SET OF INTEGRITY RULES TO ENFORCE THAT THE DATA IS CONSISTENT AND REMAINS CONSISTENT OVER TIME 3. A SET OF OPERATIONS THAT DEFINES HOW DATA IS MANIPULATED

RELATIONAL MODEL

ALLOWS END USERS TO VIEW DATA LOGICALLY NOT PHYSICALLY

TABLE 3.1

CHARACTERISTICS OF A RELATIONAL TABLE

A TABLE CAN ALSO BE REFERRED TO AS AN...

ENTITY SET

ROWS AND COLUMS

ROW (TUPLE) COLUMN (ATTRIBUTE)

KEYS

TABLE 3.3

PREDICATE LOGIC

THE RELATIONAL MODEL INTRODUCED BY E.F. CODD in 1970, IS BASED ON PREDICATE LOGIC AND SET THEORY. PREDICATE LOGIC IS EXTENSIVELY USED IN MATHEMATICS, PROVIDES A FRAMEWORK IN WHICH AN ASSERTION (STATEMENT OF FACT) CAN BE VERIFIED AS TRUE OR FLASE

Tables and Their Characteristics

The logical view of the relational database is facilitated by the creation of data relationships based on a logical construct known as a relation. Because a relation is a mathematical construct, end users find it much easier to think of a relation as a table. A table is perceived as a two-dimensional structure composed of rows and columns A table is also called a relation because the relational model's creator, E. F. Codd, used the two terms as synonyms. You can think of a table as a persistent representation of a logical relation— that is, a relation whose contents can be permanently saved for future use. As far as the table's user is concerned, a table contains a group of related entity occurrences—that is, an entity set. For example, a STUDENT table contains a collection of entity occurrences, each representing a student. For that reason, the terms entity set and table are often used interchangeably. RELATION DOES NOT MEAN RELATIONSHIP