Page 3 - Relational Databases

 Every row in the table represents a collection of related data values/record. These
rows in the table denote a real-world entity or relationship.
 Tables are related to each other through some shared attributes.
 The relationship type is shown in Relational Schema.

Component of database
 Entity
 Attribute/Column (Field)
 Domain
 Degree
 Record/Row (Tuple)
 Cardinality

Entity
 Things or object in real world with independent existence,
 In a relation each row is an entity.
 An entity may be object with:
 physical existence : person, car, house, employed, etc.
 conceptual existence : job, course, event.

Attribute(Field)
 Each entity has certain characteristics known as attributes.
 Named column of a relation.
 Example : an EMPLOYEE entity maybe describe by
employee's name, age, address, salary and job.
 Used to hold information about the objects to be represented in database.

Domain
 Set of possible values for an attribute.
 Each simple attribute of entity is associated with value set (domain of values)
 It specify the sets value that may be assigned to that attribute for each individual
entity.
 Example given an attribute named GENDER, the domains are MALE and FEMALE.
Formally written as: GENDER = {MALE, FEMALE}

Tuple/Record
 Row of a relation.

Degree
 The degree of relation is the number of attributes it contains.
 For example, Employee (employee's name, age, address, salary, job) has five
attributes or degree of Employee table is five.

Cardinality
 The number of tuples(rows) its contains.