1. Databases

2. Organise this:
Jenny is 17 and studies chemistry and physics. Tom is her best friend, he’s also 17. Her sister Jackie is friends with Sally, who is 18. Jackie is also 18. The oldest is Jim, who is 17 and also has Tom as a best friend. Jenny is engaged to be married to Tim, who is 119 and studies biology and maths. Sally and Jackie study Maths, but Sally also studies Sport, though Jackie studies three subjects, as she also takes French.

3. Probably the best way: Name Age Best friend Studying Note Jenny 17 Tom
Chem & Phys
Engaged to Tim, sister of Jackie
Jennie
No subjects given
Sally 18
Jackie
Maths and Sport
Tim
119
Biology, Maths
Age a problem?
Maths, Sport, French
Sister of Jenny

4. Note If people are best friends, then they should be connected
There is no way to “lock” best friends
Some people’s subjects get repeated, so that wastes storage space and typing time
There are several ways to write the subjects
You could wrongly enter nothing at all if it’s just a simple table
No validation has been performed, especially in the case of Tim aged 119 & Jenny/Jennie

5. A database is A persistent, organised store of data.
People depend on databases, many businesses cannot function without them.
So, the database must be
Accurate (correct)
Up-to-date (current)
Readily available to whoever needs access
Protected from people who shouldn’t have access

6. Some definitions:
Entity – the complete real-world object for which you need to hold data
Instance – one of the entities, also called a record
Attribute – a characteristic of an entity
Values – word or number information about the entity
Relationship – a connection between entities
Table – the way that most databases hold data
DBMS – a database management system – “a computer-based system to manage a database or collection of databases”

7. Examples: Entities: customers, employees, films, pupils
Instance: you, me, “Rain Man”, you
Attribute: address, gender, length, age
Value: 1 Darwin Lane, start date, 45mins, 15
Relationship: is_customer_of
Table: pupils table, teacher table (etc.)
DBMS: SIMS

8. Typical Types of Data:
Strings (text) – characters, usually up to 256 or 512 bytes long
Numbers – as integers
Real numbers – with a decimal point and maybe an displayed in a form of scientific notation
Prices – in whichever currency you want
Yes/No data (Boolean)
Dates
Times
These are all simple types, you may also see records – a compound data type, consisting of several fields of different simple types

9. Give examples of each type:
Text/string:
Integer:
Real:
Currency
Boolean
Date
Time

10. What information might you need to store about …..
A CD in a DJ’s record collection?
A candidate entering for an exam?
The same CD in a record shop like HMV?
A part in a car parts database?
An item in a supermarket database?
A customer buying travel insurance?
A pupil in a school database?
A patient in a hospital database?

11. We want to avoid: Errors Lost data Insufficient data Inconsistent data
Unauthorised access

12. Errors can result in:
Embarrassment – sending bills to dead people, for example
Financial loss – banks need everything correct
Life-or-death situations like air traffic control or airport data or navigational data for planes and ships.

13. Aims of managing a database:
Minimising storage requirements
Minimising repetition or redundancy
Fast entry of valid data
Avoidance of some verification
Fast and easy searches
Prints in neat layouts as reports

14. Data security Data integrity
Not just keeping out intruders, but also minimising the damage from:
Natural catastrophes like fire and flood
Accidental actions
Malicious actions
Data integrity
Making sure the data is accurate / correct / trustworthy
Needs validation
Software design that avoids inconsistent data

15. Validation and verification
Validation – checking that the data is valid – that is, it means something for the field it is entered into.
You could check for:
the right type
the right length
Right punctuation/syntax
Sensible values

16. How to protect data: Making backups Mirror servers Off site storage
Restricted access to buildings
Passwords on the computer
Audit trails (who did what, when)

17. Creating a database in Access:

18. Exercise Start “Access”
Create a data table for one or more of these examples: