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Relational Databases

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Relational database
data stored in tables
must put data into the correct tables
define relationship between tables
primary key
Standard Database Notation
EMPLOYEES(EmployeeID, Surname, Forename)

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Creating a database file
Design the record format for a table, considering:
­ the order of the fields;
­ the name of each field;
­ the data type for each field.
· Text (also referred to as Character or Alphanumeric);
· Number (integer, or real with a specified number of…

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Importance of Data types
Certain field types are automatically validated when the user
enters data.
­ If you have specified the field as a text field, no automatic validation
is possible.
If a field is defined as currency or numeric, no non-numeric
characters allowed
A telephone number should not be…

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Primary key
Each record in a database file needs to be given a
unique identifier - the primary key.
It needs to be carefully chosen;
­ Surname, for example, is no use as an identifier.
­ MS Access has an Autonumber data type which generates
unique identifiers automatically
The primary…

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Hierarchy of data
­ All data is stored in a computer's memory or storage devices in the form of
binary digits or bits. A bit can be either `ON' of `OFF' representing 1 or 0.
­ is a group of 8 bits. One byte can represent one character…


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