Entities “something about which an e.g.

organisation keeps data” customer

Attributes “the properties of an entity” e.g.

address

Relationships “the connections e.g. between entities”

customer

places

order

Entities

An entity may be physical:

an employee, a part, a machine

Or conceptual:

a project, an order, a course

A particular employee is an “entity occurrence” of the employee entity

Attributes

An EMPLOYEE has: A PROJECT has:

an age a project leader

a salary a start date

an address a cost

Relationships

Relationships link entities:

An employee works on a project

A part is made on a machine and appears on an order

An employee attends a course

Describing Entities and Relationships

Factory Entity (Master)

Relationship (1:many)

“makes”

Entity (Detail)Component

Relationships and Entities

Factory

Component

Given a factory

we can tell which

components it makes

Given a component

we can tell which

factory makes it

One to Many Relationships

A

B

For any occurrence of A

there may be 0,1 or many

occurrences of B

One to One Relationships

Factory Manager

Factory

Usually one entity should be an attribute of the other

Sometimes the diagram requires one-to-one

Many to Many Relationships

component order

One component

appears on

Many orders

One order Is for

Many components

A database to track motorbike maintenance.

In the databases described by the following 2 LDS's, a player's performance in matches is recorded, from slightly different perspectives.

Exercise: Data Modelling• 1. A customer purchasing a lot of order from the salesperson

• 2. Two accountants preparing the sales reports to the senior managers

• 3. A credit card holder have the following personal information: name, address, age

• 4. A school had a lot of departments such as IT, Accounting, Math's, etc. Each department is consists of 6 lecturers. Each lecturer handles maximum of two classes in one day. Each class could only accommodate maximum of 40 students.

Exercise :DFD• Travel Agency

A travel agency arranges holidays for customers. Bookings are made directly by customers. When a customer makes an approach, the reservations clerk selects appropriate flight details and hotel details from lists which are regularly updated. The details are entered onto a Provisional Booking file.

The customer must confirm this booking within three days by sending a deposit of 10% of the costs. On receipt of the deposit, Reservations transfer the details from the Provisional Bookings file to the Full Bookings file.

Four weeks before the flight is due, Accounts send an invoice to the customer for the remaining costs. Accounts notify Customer services when the full payment is received, and Customer Services then send tickets and joining instructions to the customer.

JSP

JSP

Counts the number of times words occur in a file

Counts the number of times words occur in a file

Flowchart Exercises

If student's grade is greater than or equal to 60Print "passed“ else Print "failed“

Create a flowchart for Adding two numbers

Create a flowchart for inputting your employee’s name. If the first letter starts from A to J then display “ First Category” , if K to T then display “ Second Category” otherwise display Third Category

Set the counter to 0. If the counter is more than 10 then customer receives free value meal otherwise no free value meal.

Flowchart ExerciseSet total to zeroSet grade counter to oneWhile grade counter is less than or equal to ten• Input the next grade• Add the grade into the total • Set the class average to the total divided by ten• Print the class average.

End