1. Databases

2. What is a database? A database is a collection of data
Maybe computerised
Will be organised so as to make the retrieval and maintenance of data as easy as possible
A computerised database:
Offers the great advantage of speed
More sophisticated databases will use database management software
MS Access is an RDBMS – Relational Database Management System

3. Flat files A flat file is a database held in a single file
The data stored in one file cannot easily be linked to data stored in another file.
These so-called ‘flat files’ are useful for:
a list of contact names and addresses
a list of student grades
details of a video collection.
A spreadsheet can be used as a flat file database, with a column representing a field and a row representing a record.

4. Flat file problems Redundant data – repetition of the same data
makes the file larger than necessary
wastes space on disk
makes it slow to retrieve information
Errors arising from typing the same data many times in different records
Typographical errors occur
Loss of data consistency
Difficulties in updating and modifying data
All occurrences would have to be located and changed

5. Solving the flat file problems
Study this flat file data for a moment
Identify some of the problems that have occurred
Consider how multiple tables would improve the database for this orders flat file

6. Multiple tables Each entity should have its own table
Each record must have a unique ID.
This is the principle behind relational databases.
The following tables would be created from the previous flat file

7. Multiple tables
This would then mean that the orders table would look like:
In reality, the supplier data in the Products table would be regarded as a separate entity and have its own table
Why is price retained as a field in the orders table?

8. Database system .v. flat file
data independence
structure of the database does not affect the programs which access the database
quality of management information
information more useful as it is based on a single, comprehensive set of data
control over redundancy
data is not stored several times in separate files
consistency of data
because data is only stored once, no possibility of holding different data on different files (e.g. different addresses for the same employee)

9. Database system .v. flat file (cont.)
more information available to users
because the data is held in a single, company-wide database, all users have access to it
greater security of data
users can only view or update the parts they are authorised to access or change
less time spent inputting data
because it is held only once, there is no duplication of effort inputting the same data into different files.