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Databases

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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…

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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…

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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…

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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

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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

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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?

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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…

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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…

Comments

Mr A Gibson

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A succinct introduction to databases, including flat file vs. relational with a worked example. Keep reviewing this so you understand the process of normalisation.

Dylanfletchdog

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cool

helped me alot????

SamHendo

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my name jeff

iRapChiz

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SOOO Useful

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