In early computer business systems data was stored similarly to paper based filing systems in separate files by business departments. This was due to familiarity with old paper systems and was limited by sequential storage on data tapes in early computers. However, this file centred approach caused problems with:
- Data duplication
- Updating information across multiple files
- Difficult to cross reference data
To overcome this limitation a form of centralized and comprehensive data organization was developed and administered using a database management systems (DBMS). The centralization of data allowed exploitation of relationships across the dataset resulting in the term relational database. The benefits being:
- Comprehensive dataset
- Centralized administration with single point control of access, security and backups
- Data can be edited by multiple users improving the consistency and correctness – all users benefit from this single comprehensive view
- Data and physical computer resources are separated giving the user a logical view independent of hardware platform
A relational database stores data as sets of tables containing 2 columns of information. To ensure that the data held in each row is unique a primary key is held. Often this is simply a sequential index number starting with 1 and incrementing with each new row of data added. To relate tables a foreign key is used which numerically identifies a link to the relevant other table in the database.
To access relational data SQL (Structured Query Language) is used to create commands which select and display the required data. The most commonly used SQL instruction is the “select” command e.g.
SELECT surname, salary
FROM employee
WHERE department = engineering AND salary >= 40000
ORDER BY salary
would display columns for “surname and salary” from the “employee” database in salary order for those engineers paid 40000 or more.
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