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Define each of the following terms:
- entity type
- entity-relationship model
- entity instance
- Attribute
- relationship type
- strong entity type
- multivalued attribute
- associative entity
- cardinality constraint
- weak entity
- binary relationship
- derived attribute
- business rule
(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.
(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).
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
(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.
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