Chapter 2, Problem 2.1RQ

Define each of the following terms:

1. entity type
2. entity-relationship model
3. entity instance
4. Attribute
5. relationship type
6. strong entity type
7. multivalued attribute
8. associative entity
9. cardinality constraint
10. weak entity
11. binary relationship
12. derived attribute
13. business rule

Program Plan Intro

(a)

Definition of Entity type.

Explanation of Solution

Entity type can be defined as a set of entities which share some common characteristics, behavior and attributes.

Program Plan Intro

(b)

Definition of Entity-relational model.

Explanation of Solution

Entity-relational model represents the logical relationship between the entities and attributes in the database for an organization. it helps in creating database easily and can be understood by all. E-R model can be expressed as entity-relationship diagram also called as (ERD diagram).

Program Plan Intro

(c)

Definition of entity instance.

Explanation of Solution

Entity instance is single occurrence of entity type. Consider an example, suppose employee is an entity type which has many instances. Example of instances can be John, Jenny or any other employee.

Program Plan Intro

(d)

Definition of attribute.

Explanation of Solution

Every entity instance or set has its own attributes. Attributes state the behavior and characteristics of the entity. consider an example of employee here employee is the entity set that consists of various attributes such as name, address, location, employee id, mobile number etc., which states the characteristics of the entity instance or set.

Program Plan Intro

(e)

Definition of relationship type.

Explanation of Solution

Relationship type is the meaningful representation of data between the entity set. It is of four types:

i) one to one relationship: in this type of relationship, one record of the table is associated with one record of another table.

ii) one to many relationships: In this type of relationship, one record of first table can be associated with N numbers of records of the other table.

iii) many to one relationship: In this type of relationship, many or N number of records of the first table can be associated with one record of the other table.

iv) many to many relationshipsIn this type of relationship N number of records of first table can be associated with N numbers of records of the other table.

Program Plan Intro

(f)

Definition of Strong entity type.

Explanation of Solution

Strong entity type: Strong entity is an entity which is not dependent on any other entity. For example, tire can be considered as an example of the strong entity as its existence does not depend on any vehicle entity set.

Program Plan Intro

(g)

Definition of multi-valued attribute.

Explanation of Solution

Multivalued attributes are those which takes some values from the entity instance. For example, in the employee entity set address is a multi-value attribute it can hold the permanent and temporary address of the employee.

Program Plan Intro

(h)

Definition of associative entity.

Explanation of Solution

Associative entity provides association between the given entity set or instance. An entity is associative only if it has all the entity set or instance involved in the many relationships. The result associative entity should be independent.

Program Plan Intro

(i)

Definition of cardinality constraints.

Explanation of Solution

Cardinality constraints specify the number of elements associated with each other between the two tables. It can be of two types; minimum cardinality and maximum cardinality.

Program Plan Intro

(j)

Definition of weak entity.

Explanation of Solution

Weak entity depends on another entity for its existence. And it has no importance or existence if the dependent entity does not exist. Example of weak entity can be room, as it depends on building and can exist only if there is any building.

Program Plan Intro

(k)

Definition of Binary relationship.

Explanation of Solution

Binary relationship is used between the instances of two types and are among the most common types of relationship encountered. It supports three types of cardinalities:

i) one to one: consider an example of employee, each employee has its own parking area. Or we can say that the parking area is assigned to the employee.

ii) one to many: it indicates that one product is connected to others through a common product line.

iii) many to many: many students can do many courses and vice versa.

Program Plan Intro

(l)

Definition of Derived attribute.

Explanation of Solution

Derived attribute can be calculated by using the related attributes. Suppose we must find the tenure of an employee, to find age, we need the date of birth and the date of joining of the employee. Thus, tenure of an employee is a derived attribute.

Program Plan Intro

(m)

Definition of business rule.

Explanation of Solution

Business rules are used to provide direction to business and help to lead the progress of the business project. Some business rules are important as they provide logical schema. Database designers need to follow the business rules during the development of the database as per the directions provided by the honor of code. These rules are also used for maintaining the integrity and accuracy of data.