Originally, the Data and the Application Software were combined, making it difficult to share data between different parts of an organisation. This lead to the development of databases.
A database is
a collection of non-redundant data shareable between different applications.
There are 3 key terms for all databases you need to know:
A field is an item of data stored because it is of interest to the user.
A record is a collection of fields relating to the same subject.
A file is a collection of similar records.
Single table database, with separate copies of data in each part of the business.
e.g a phone directory
Data Duplication
Data is repeated and hence stored many times.
This wastes disk space and slows down query time.
Program-data dependence
Maintenance
Every occurrence of a piece of data will have to be updated if its value changes
More Manual data entry required and therefore a greater likelihood of errors when data is being entered.
The solution to these problems was to divide the data into logical groups and store the data in multiple tables, then connect (relate) the tables to each other; a Relational database.
Organisations started to use databases to store their data in an organised way, so that it could later be retrieved very quickly.
Computers were able to process data much faster than humans, as they can do millions/billions of calculations per second (MHz /GHz).
A Relational database is a colllection of related files organized
Characteristics of a Relational Database
Data is stored in a set of tables
Tables are joined by relational links
Reduces duplication of data in database
Data is 'Normalised'
Allows greater flexibility and efficiency
Each table must have a unique reference for each record, called the Primary key
e.g. A car registration number plate uniquely identifies the car
This may be a single data item or a combination of data items.
A Composite Primary Key is where the PK consists of several data items
e.g. Student_First_Name, Date of Birth
Linking a PK to other tables creates the Foreign key
These foreign keys form the Relationships that link the tables together
a. describe flat file and relational databases, explaining the differences between them;
Definitions of both, key features, advantages and disadvantages
b. design a simple relational database to the third normal form (3NF),
using entity-relationship (E-R) diagrams and decomposition;
c. define, and explain the purpose of Primary, Secondary and Foreign Keys;
d. describe the structure of a DBMS including the function and purpose of :
Data Dictionary,
Data Definition Language (DDL) and
Data Manipulation Language (DML);