1. Relational Databases

2. What is a database?
An organized collection of records presented in a standardised format searched by computers
A collection of related data stored in one or more computerised files in a manner that can be accessed by users or computer programs via a database management system

3. Computer Databases
Types of database-
Flat file
Relational

4. Flat file
The simplest type of database where data is stored in rows & columns
Each row represents an instance or “record”
Each column represents an “attribute” or piece of data about that instance
Easy for us to build in Access or Excel

5. Flat file example
Attribute or Field
Instance or Record

6. Relational
Data is divided into tables which are ‘related’ together.

7. Key Terms
Entities are real life objects represented in the database. We know them as TABLES
Examples: customer, product, invoice.
Attributes are individual pieces of data about each entity. We know them as FIELDS
Examples: customer name, product ID, invoice number, order date.
If there are just the two entities then the other pieces of data are the attributes of this entity. For example:
Artist name
Artist DOB
Artist country of origin
Artist current location
Track name
Track length
Track release date
Track genre
Track rating
Track position reached
are all the attributes and I’ve added in the entity bit also so that it’s really clear to see what attribute ‘belongs to’ which entity

8. Instances or records
Each row entry into this flat file database is called an ‘instance’ as it is an actual instance of the data occurring.
This collection of pieces of data belonging to the one instance is more commonly referred to as a ‘RECORD.
Attributes or Fields
So every time you entered in a row of data into your flat file database you have created a record or instance
Instances or
Records

9. Uniquely identifying an instance
Usually one primary key attribute is used to uniquely identify the instance (or record) of an entity
What are suitable primary key attributes for the following entities?
Product Order
Customer Sales Person
Why are these necessary?
Why do we not just use the business or person name?

10. What does this means to the user?
Redundant data
Redundant data is any data that has more than one copy of it in the database or in other words it is duplicate data
What does this means to the user?
Think about:
server space/memory
the ease of updating this data
if it is stored in more then one place

11. Let us consider music data recorded in a flat file database:
Designing the tables in a relational database Entities and their attributes
Designing and making a relational database reduces this redundant data.
Let us consider music data recorded in a flat file database:
Track name
Track position reached
Track rating
Track genre
Track release date
Track length
Track ID
Artist name
Artist Current Location
Artist country of Origin
Artist DOB
Artist ID
These two boxes show my
list of attributes for the
entities ‘track’ and ‘artist’
You may want to re-arrange your flat file data so that it corresponds to this clear idea

12. Can a track belong to more than one artist?
Designing the tables in a relational database The relationships between entities
What is the relationship between the instances of data for each of the two entities (the boxes on the last slide)?
In other words what is the relationship between one individual track and one artist?
Can a track belong to more than one artist?
Can an artist have more than one track?
Look at the data for the artist and look at the data for the track – how are these things related to each other? It may help to just look at one record/instance in your flat file database.
How a relational database reduces redundant data 2
Often, a relational database has multiple tables in it each one representing an entity
This means that the instances (data records) are usually stored once and then referred to

13. identify each instance
Designing the tables in a relational database Defining the relationships
The relationship between the instances of data for each of the entities tells us how the entities are linked to each other.
For example we can think about vehicle ownership in the UK .
Here is a car and its owner What is their relationship?
Instance of a ‘Vehicle’ entity Instance of a ‘Person’ entity
Some attributes: Some attributes:
Reg: CA51 ABC NI No: JG021316A
Brand: Audi Ethnicity: Caucasian
Model: Q7 Gender: Female
Colour: Blue Hair colour: Brown
Year: DOB: 06/04/82
There is a ‘Car’ entity and a ‘Person’ entity which have various attributes and a unique ID – the car registration number and the person’s National Insurance number used to uniquely identify each individual person or car (each instance of the ‘Car’ or ‘Person’ entity).
Unique way to
identify each instance

14. Designing the tables in a relational database Relationship cardinality example
The relationship between the instances of the vehicle entity and the instances of the person entity can be stated as:
One vehicle instance can only have one owner (person)
One person instance is allowed to own one or more vehicles.
This value to the relationship between the individual instances of each entity is called the relationship cardinality and can be shown as:
This diagram is from the SSADM notation for database design and is part of an Entity Relationship Diagram (ERD). Yes it does seem odd that the lines indicating a multiple or solo relationship are at the opposite ends of the diagram but this is the correct way of doing this. There are other ways to model relationships between entities including
IDEF1X
Bachman notation
Martin notation
The (min, max)-notation of Abrial
UML
EXPRESS
The cardinality of a set is a measure of the "number of elements of the set“ so this means that the cardinality of the instances of one entity in a relationship
Person
Vehicle
Owns
This line shows that an instance of the vehicle entity can have a relationship with one instance of the person entity
This crows foot notation shows that at an instance of the person entity can have a relationship with one or more instances of the vehicle entity
Relationship name goes in a diamond

15. > > PROGRESS CHECK < <
Designing the tables in a relational database Using the relationship to plan the tables
> > PROGRESS CHECK < <
So we now know the relationship cardinality between the entities ‘Person’
and ‘Vehicle’ and we know each Primary Key and some of their attributes
How does this information help us with the tables we need to create? If we were to design the two tables they would contain these attributes: But they are not yet linked together and the relationship has not been created
Vehicle Table
Registration Number
Brand
Model
Colour
Year
Person Table
National Insurance No
Ethnicity
Gender
Hair colour
DOB

16. Designing the tables in a relational database The Primary Key is the key to a good relationship!
To create a relationship between these two tables (and therefore create a relational database) we need to use a primary key (PK) from one table and place it as a foreign key (FK) in the other table.
Doing this allows us to then link this one duplicate attribute which is in both tables and create a relationship between the two tables

17. Let’s look at this logically. We have 2 options:
Designing the tables in a relational database Choosing which Primary Key
Let’s look at this logically. We have 2 options:
to take the PK from the vehicle table and put it as a FK in the person table
to take the PK from the person table and put it as a FK in the vehicle table
It is good to consider some example data to see this in reality. The woman in the scenario also owns this car,
a green Fiat Punto: example data is on the next slide

18. Lots of Data Redundancy! Person Table Vehicle Table
Designing the tables in a relational database Choosing which Primary Key – Option 1
Person Table
NI No
Ethnicity
Gender
Hair Colour
DOB
Vehicle Reg No
JG021316A
Caucasian
Female
Brown
06/04/82
CA51 ABC
GH65 GYT
BV677514I
Oriental
Male
Black
23/02/75
BS45 HJJ
FT121285Y
African
03/06/90
HT7 UKK
OPTION 1
Take the PK from
the vehicle table
and put it as a FK
in the person table
example data
Lots of
Data
Redundancy!
Every instance entry in the
Vehicle table would result in a
complete instance record being
entered into the Person table
Vehicle Table
Registration
Brand
Model
Colour
Year
CA51 ABC
Audi Q7
Blue
2006
GH65 GYT
Fiat
Punto
Green
2002
BS45 HJJ
Rover 75
Scarlet
1996
HT7 UKK
Ford
Orion
Grey
1986

19. The only duplicate data
Designing the tables in a relational database Choosing which Primary Key – Option 2
Person Table
NI No
Ethnicity
Gender
Hair Colour
DOB
JG021316A
Caucasian
Female
Brown
06/04/82
BV677514I
Oriental
Male
Black
23/02/75
FT121285Y
African
03/06/90
OPTION 2
Take the PK from
the person table
and put it as a FK
in the vehicle table
example data
Vehicle Table
Registration
Brand
Model
Colour
Year
Owner NI No.
CA51 ABC
Audi Q7
Blue
2006
JG021316A
GH65 GYT
Fiat
Punto
Green
2002
BS45 HJJ
Rover 75
Scarlet
1996
BV677514I
HT7 UKK
Ford
Orion
Grey
1986
FT121285Y
Minimal
Data
Redundancy!
The only duplicate data
is correctly in the
foreign key column

20. Designing the tables in a relational database Choosing the Primary Key and using it
We select Option 2 to reduce duplicate data and therefore save memory in our database
So we take the Primary Key from the person table and put it as a Foreign key in the vehicle table and now our table attributes planning is:
Vehicle Table
Registration Number
Brand
Model
Colour
Year
Owner NI Number
Person Table
National Insurance No
Ethnicity
Gender
Hair colour
DOB

21. Designing the tables in a relational database 1 to many relationship cardinality and the primary key
In a one to many relationship between entities it is quick to learn which Primary key to use.
It is always the Primary Key of the entity that is on the one end being used as a Foreign Key of the entity that is on the many end
NOTE: ‘one or more’ and ‘many’ are often interchangeable when used in relationships
The way I remember this cardinality and keys rule is to say to myself “one gives to many” meaning that the ‘one’ end entity gives their primary key to the ‘many’ end entity and it is their foreign key
Person
Vehicle
Owns