Database: Relational Vs Flat File

Databases - Structure

• Flat file database, contains only one table• Relational database, contains more than

one table where relationships exist between the data in the table

• A flat file database often suffers from inefficient repetition of data.

• Normalisation is the process of removing this repetition by crafting relationships between tables.

Databases – Flat File Vs Relational Database

Name Department Boss Phone

Smith Sales Britney Lurgi 9123 456

Jones Sales Britney Lurgi 9123 456

Lennon Sales Britney Lurgi 9123 456

Sade Transport Tom Brick 9876 543

Masoch Transport Tom Brick 9876 543

STAFF TABLE

Name Department

Smith Sales

Jones Sales

Lennon Sales

Sade Transport

Masoch Transport

DEPARTMENTS TABLE

Department Boss Phone

Sales Britney Lurgi 9123 456

Transport Tom Brick 9876 543

+ No unnecessary data repetition

+ Department info easily modified in one operation.

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Types of Relationships, connection between data

• One-to-one relationship:

Eg. Airline’s passenger details:

passengers Seats1

Each passenger has only one seat and each seat can be assigned to only one passenger.

A record in one table is connected to only one record in a second table.

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Types of Relationships, connection between data

• One-to-many relationship:• Eg. customer details & job quotation:

The one supplier can provide MANY products, but each product comesfrom ONE supplier.Also, eg. several workers share single telephone extensions; each extension record is related to several employee’s records.

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Types of Relationships, connection between data

• many-to-many relationship:• Eg. Student details and subjects tables:

Each student studies many subjects and each subject has many students

students subjects

Databases – Flat File Vs Relational

• School and Student Details• If data was only in one table, with fields of

surname, fname, school, address, phone no, fax no, etc. What would be the consequence of a school changing its phone number?

• A RDMS with two tables, one with student info and one with school information will avoid this duplication.

Databases – Flat File Vs Relational

• Advantages of a relational database:– reduced data redundancy – unnecessary

duplication of data– improved data integrity or accuracy of data– able to access the data from separate but

related tables or files very quickly and simply– allows easy querying, reporting, etc.