Where do databases come from?
- There may be an manual system that has reached the limits of its usefulness
- processing requirements of the organization may have proved to be beyond the capabilities of flat file system
- processing requirements of the organization may have proved to be beyond the capabilities of flat file system
Why is database design important?
- Look at the following Excel spreadsheet currently used Look at the following Excel spreadsheet currently used by ABC Ltd to store its course information.
- need to keep record of staff members who attend each course- uses a list on Excel worksheet, simple arrangement (rows and columns)
- single table
- it may be better to break it up into separate lists, but lack the ability to hold cross-reference in Excel.
- Columns headed Atendee1 name and Atendee1
Problems with this approach
Redundant data
- each time that staff member attends a course it is necessary to record their department.
- This redundancy could be avoided if information about the staff member could be held in a separate list that could be crossreferenced.
- each row contains a code for the course as well as its title. This redundancy could be avoided if information about the course could be held in a separate list that could be cross-referenced.
- redundant data should not be confused with duplicate values.
- This redundancy could be avoided if information about the staff member could be held in a separate list that could be crossreferenced.
- each row contains a code for the course as well as its title. This redundancy could be avoided if information about the course could be held in a separate list that could be cross-referenced.
- redundant data should not be confused with duplicate values.
Inflexibility Inflexibility
- it is necessary to impose arbitrary limits on its uses
- waste of storage space
- the ways that can analyse the data in this example are limited.
Limited sharing of data
- file is manipulated as a single unit.
- it is not possible for more than one user to update the data in
the same file at the same time.
- it is not possible for more than one user to update the data in
the same file at the same time.
No inherent control for data quality
- In flat file systems, it is necessary to write logic into an application to ensure the quality of the data
- such application logic may have to be rewritten every time the design of the file is changed
- In flat file systems, it is necessary to write logic into an application to ensure the quality of the data
- such application logic may have to be rewritten every time the design of the file is changed
Changing the data can lead to unexpected results
- update anomaly , ‘every occurrences should be updated
- insertion anomaly, ‘difficult to find missing data ’
- deletion anomaly, ‘loss all the information when it deleted'
- insertion anomaly, ‘difficult to find missing data ’
- deletion anomaly, ‘loss all the information when it deleted'
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