StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

From data model to database

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

Mapping the ERD onto a database

Rules for assigning attributes to relations

Relations must be well-normalised– No repeating groups– Every determinant in a relation must

be a candidate identifier of that relation

Where there is a choice, avoid relations where attributes will have null values

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:1 relationships - total participation (1)

Create a single relation

Department( Dept#, Dept_Name, Faculty, Head)

Department HeadHas a1 1

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:1 relationships - total participation (2)

Dept# Dept_Name Faculty Head

10 History A Jones

20 Sociology B Smith

30 Maths C Edwards

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:1 relationships - membership of one entity

partial (1)PILOTS is a list of available pilots who do not have to take weekly flights

Create two relations

‘Post’ pilot number to Weekly Flights relation

WeeklyFlight

Pilot1 1

Has a

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:1 relationships - membership of one entity

partial (2)Weekly Flights

Pilots

Flight# Date of Dep. Pilot#

BA123 22-Oct-96 P10DL567 24-Oct-96 P20

Pilot# Pilot Name Address

P10 James Address_AP15 MacDonald Address_BP20 Green Address_C

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:M relationship - total participation (1)

Create two relations

‘Post’ department number to employees relation(Also appropriate for situation where ‘1’ entity type is partial - eg when department has no employees)

Department EmployeeHas1 M

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:M relationship - total participation (2)

Department

Employees

Dept# Dept Name Location

1 History Arts2 English Arts3 Geography Geog

Emp# Emp Name Date of Appt Dept#

100 Lee 9/75 1200 Smith 10/80 1300 Adams 1/80 3400 Sharma 3/90 2

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:M relationship ‘many’ entity type partial (1)

Employees do not have to belong to a department

Create a new relation to record relationships

Department Employee1 M

Has

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

1:M relationship ‘many’ entity type partial (2)

Department

Employees

Dept# Dept Name Location

1 History Arts2 English Arts3 Geography Geog

Emp# Emp Name Date of Appt

100 Lee 9/75200 Smith 10/80300 Adams 1/80400 Sharma 3/90500 Jones 1/87

Emp# Dept#

100 1200 1300 3400 2

Emp_Dept

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

M:N relationship (1)

Create a new relation to record the relationship

Appropriate for both types of participation on either ‘side’

Student ModuleM N

Take

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

M:N relationship (2)

Students

Student_Modules

Stud# Stud Name DOB

1 Lee 19722 Smith 19743 Adams 19734 Sharma 1972

Mod# Stud# Year Grade

cm103-5 1 1996 Ccm506-1 1 1996 Ecm506-1 2 1995 Bcm780-3 3 1996 Bcm103-5 4 1997 A

Mod# Module Name

cm103-5 PSADcm206-6 DBMScm506-1 IBIScm780-3 SDM

Modules

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

Mapping Supertypes/Subtypes onto

a database (1)

Can be mapped onto a database in two ways

Under-graduate

Post-graduate

d

Student

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

Mapping Supertypes/Subtypes onto

a database (2)Either:Student( Stud#, Stud_Name, DOB, DOE,

Student_Type)Undergrad( Stud#, Module#, Year, Grade)Postgrad( Stud#, Degree, Thesis_Title)

ORUndergrad( Stud#, Stud_Name, DOB, DOE, Module#,

Year, Grade)Postgrad( Stud#, Stud_Name, DOB, DOE, Degree,

Thesis_Title)

StaffordshireUNIVERSITY

Schoolof

Computing

Dr. Andy Seddon

Summary

Draw up enterprise rules– interviews– questionnaires etc.

Construct E-R model and ERD Map E-R model onto database i.e. write

database schema Check relations are in BCNF If not, create new relations which are in

BCNF