AS ICT Notes Ch. 5 - G061

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Varun Pratap
Chapter 5
Database: is a collection of related data items. E.g An address book, a register at a school
A Database is made up of files (one or more)
Table is a file that contain information about entities, it is made up of rows and columns
An Entity is the overall name for the contents of a table. It should be in capitals e.g
WORK_COLLEAGUES
An Attribute is a field; it can be a primary key or foreign key
Primary Key is a field in a table which is unique and helps you identify every record in that table
A Composite Key is when not a single field is appropriate to be used as a primary key therefore two
or more fields can be combines to make a primary key.
A Foreign Key is a field in a table; it is a primary key in another table
Duplicate Data: when data has been repeated more than once
Disadvantages of duplicate data:
- Increases storage space required
- Makes errors more likely to occur
- Breaks rules of normalisation
Referential Integrity: The values found in the table with the foreign key field have a corresponding
value in the table with the primary key

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Relationship is linking together entities e.…read more

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· Databases require a lot of editing and deleting of data
· Databases that store previously collected data need to break the rules of normalisation
Data Dictionary contains descriptions of the key items in a database e.…read more

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