1. Topic 3: Data
Databases

2. Storing Data
When it comes to storing data, we have different ways of storing it
Each way of storage is thought of as a different structure of data
These different structures include
Saving pure text files with paragraphs of information
Storing data in an XML (Extensible Markup Language) file
Keeping data in a series of tables
Data: Databases

3. Storing Data These different structures have specific names
Unstructured
When we save data with no structure at all
Like paragraphs in a text file
Makes finding information inside difficult (as we have to read everything)
Data: Databases

4. Storing Data Semi-Structured
When our data has some structure, but is still difficult to read/understand
Most commonly seen in markup languages
Like HTML or XML
We still follow some structure, but we still have freedom to change this structure as needed
Structured
When our data has a very rigid and defined structure (that we can’t easily change)
Commonly seen when storing data in tables (with rows and columns)
Makes it very easy to find something (as we find the row/column we need)
Data: Databases

5. Data Models
Databases are used whenever we want to store lots of structured data
Literally the base of our data
Can come in lots of different formats (each one changing how we use it)
Relational
Factual
Flat-format
We will be looking at relational databases
Data: Databases

6. Data Models
Before creating any data, or any structures for the data, we first analyse the requirements of the database
This comes into play in two ways
The data requirements
What data do things need in total
For example, a classroom needs a classroom code, year group, and teacher
The data constraints
What can the data not do, or not be grouped with
For example, a classroom cannot have more than one teacher
Data: Databases

7. Data Models Relational databases work based off of two things
The entities that the database contains
The relationship between these entities
These types of databases are designed to accurately reflect the world
By identifying relationships between entities
We can use these to plan out a Conceptual Data Model of the database
Entity
A single place, person, or thing about which data can be stored
Data: Databases

8. Data Models Each entity can also have data associated with them
Each piece of data fitting into a property, also known as an attribute
For example, a Person entity might have the following attributes
Name
Age
Gender
Databases contain many records of an entity for each individual person/place/thing
Each record is known as an instance, or occurrence
Data: Databases

9. Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data Models
We can write entities out, with their attributes, in a simple description
For example, a Student has a First Name, Surname, Date of Birth, and Current Form Group
We can describe this entity using the following:
Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data: Databases

10. Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data Models
All entities need one attribute (or a combination of them) the uniquely identify them
This is known as the Entity Identifier
We can either add an attribute specifically for this (like an ID), or use a combination of attributes (like a first and last name)
Note that entity identifiers should be unique among all entities of one type
Here’s an example (the underlined attributes combine to make the entity identifier)
Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data: Databases

11. Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data Models
The individual attributes on their own would be too weak to use as an identifier
As there could by many students with the same first name
However, lots of them combined are more appropriate
As the chance of finding a student with all three being the same are negligible
Student(FirstName, Surname, DateOfBirth, CurrentFormGroup)
Data: Databases

12. Create a data model for the following situation, and write the entity descriptions the model would use:
A system administrator is creating a database for a university. They need to store information about the modules they offer, the professors that teach those modules, and the students that enrol onto those modules. Module have their module ID, their name, and branching subject (like Maths, Computer Science, Art, and so on). Professors have their name and faculty ID. Students have their name, date of birth, course enrolment (like Microbiology, Computer Science and Maths, Software Engineering) and module enrolment.
Data: Databases

13. Data Models
We can represent entities (and their attributes) in a visual format
Each rectangle is an entity, and the lines inside them are their attributes
Where the entity identifier is underlined
Can be referred to as an entity diagram
Data: Databases

14. For the data model you made in the previous exercise
Create an entity diagram for each entity
Remember to underline the entity identifier for that entity
Data: Databases

15. Entity Relationships
A relationship is an association between two entities
Like a House and a Person
A House could contain multiple People
Relationships have degrees (known as cardinalities), defining the maximum number of entities one entity can be linked to
One-to-One
One-to-Many
Many-to-Many
Data: Databases

16. Entity Relationships Here are some examples of cardinalities in action
Primary care physicians will help many patients
One-to-Many
Surgeons perform operations
Many-to-Many
Patients have health-care cards
One-to-One
Data: Databases

17. For your data model from before, think about what relationships it would use
And the cardinalities of them
A system administrator is creating a database for a university. They need to store information about the modules they offer, the professors that teach those modules, and the students that enrol onto those modules. Module have their module ID, their name, and branching subject (like Maths, Computer Science, Art, and so on). Professors have their name and faculty ID. Students have their name, date of birth, course enrolment (like Microbiology, Computer Science and Maths, Software Engineering) and module enrolment.
Data: Databases

18. Entity Relationships
We can represent relationships between entities in a visual format
Making use of entity diagrams
Data: Databases

19. Entity Relationships These lines have specific start and end points
Each representing a different cardinality
Data: Databases

20. Entity Relationships
We can flesh out the relationship diagram with entity diagrams to create the full Entity Relationship (ER) Diagram
Data: Databases

21. Create an ER Diagram using the data model, entity descriptions, and relationships you made for this situation
A system administrator is creating a database for a university. They need to store information about the modules they offer, the professors that teach those modules, and the students that enrol onto those modules. Module have their module ID, their name, and branching subject (like Maths, Computer Science, Art, and so on). Professors have their name and faculty ID. Students have their name, date of birth, course enrolment (like Microbiology, Computer Science and Maths, Software Engineering) and module enrolment.
Data: Databases

22. Relational Data Models
These kinds of models are based on mathematics
Using the idea of a relation
For example, we have two sets
𝑇𝑒𝑎𝑐ℎ𝑖𝑛𝑔𝑆𝑡𝑎𝑓𝑓={𝑀𝑟 𝐴, 𝑀𝑟𝑠 𝐵, 𝑀𝑟 𝐶}
𝑀𝑜𝑑𝑢𝑙𝑒𝑠={𝑃𝑟𝑜𝑔𝑟𝑎𝑚𝑚𝑖𝑛𝑔 101, 𝐿𝑖𝑛𝑒𝑎𝑟 𝐴𝑙𝑔𝑒𝑏𝑟𝑎, 𝐺𝑒𝑛𝑒𝑡𝑖𝑐 𝐶𝑜𝑚𝑝𝑢𝑡𝑖𝑛𝑔}
We can form a relation of these (creating their own set)
𝐴𝑠𝑠𝑖𝑔𝑛𝑇𝑒𝑎𝑐ℎ𝑒𝑟𝑠= 𝑀𝑟 𝐴, 𝐿𝑖𝑛𝑒𝑎𝑟 𝐴𝑙𝑔𝑒𝑏𝑟𝑎 , 𝑀𝑟𝑠 𝐵, 𝐺𝑒𝑛𝑒𝑡𝑖𝑐 𝐶𝑜𝑚𝑝𝑢𝑡𝑖𝑛𝑔 , 𝑀𝑟 𝐶, 𝑃𝑟𝑜𝑔𝑟𝑎𝑚𝑚𝑖𝑛𝑔 101
Data: Databases

23. Relational Data Models
In these models, we would represent entities as tables
Every column in the table being an attribute of that entity
Every row in the table being an instance/occurrence of that entity
The underlined column is the entity identifier
ModuleCode
ModuleName
TotalCredits
NumberOfLessons
HoursPerLesson
PRO101
Programming 101 10 12 1
LIN001
Linear Algebra
GEN001
Genetic Computing 20 24 2
Data: Databases

24. Based off this relational data model for a Module table
Come up with a relational data model for a Teacher table
Should include the teacher’s ID, name, start date, and assigned modules
Come up with at least three occurrences to put in the table
ModuleCode
ModuleName
TotalCredits
NumberOfLessons
HoursPerLesson
PRO101
Programming 101 10 12 1
LIN001
Linear Algebra
GEN001
Genetic Computing 20 24 2
Data: Databases

25. Relational Data Models
You may have come up with something like this for the Teacher table
With both of these tables together, we have an implicit relation
As the Teacher table refers to AssignedModules
Which are the ModuleCode values from the Module table ID
FirstName
LastName
StartDate
AssignedModules
Johnathan
Joseph
02/04/1999
PRO101, MAL002
Abi
Pranav
16/06/2010
LIN001, ALG001
Clive
Sinclair
21/03/1990
GEN001
Data: Databases

26. Relational Data Models
We have to link data from one table to another to create a relation
The type of relation depends on where and how the values are used
The entity identifier is referred to as the Primary Key (when in its own table)
When this is used in another table, we call it the Foreign Key
In our example earlier, the AssignedModules is the Foreign Key for the ModuleCode
Data: Databases