OCR AS ICT Unit 1 Chapter 5


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  • Created by: Sqd3
  • Created on: 18-04-14 13:08

Chapter 5 - Database Terminology

Table (Entity) - A data structure made up of rows and columns containing data about items and must have a unique name (inc. fields and records).

Record - A single row within a table that contains data about a single item/event.

Field (Attribute) - An individual data item within a record and holds a single data item.

Primary Key - A unique identifier for a field in a record.

  • Simple Primary Key - Made up of a single field only.
  • Compound Primary Key - Combines more than one field to make a unique value.

Foreign Key - A field in one table that is linked to a primary key in another, used to link tables together. (data types must be the same)

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Chapter 5 - Database Terminology

Referential Integrity - The values found in the table with the foreign key field which have a corresponding value in the table with the primary key. It makes sure that it's not possible to enter a reference in a database to a link which doesn't exist.

Duplicate Data - When data has been repeated more than once.

  • Increases storage space required.
  • Makes errors more likely.
  • Breaks rules of nromalisation.


Relationships - The links between fields in different tables.

  • One-to-One
  • One-to-Many
  • Many-to-Many
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Chapter 5 - Relationships


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Chapter 5 - Normalisation

Normalisation - A process applied to data structures to lower redundancy and to increase its integrity.

First Normal Form (1NF):

  • Each table have a primary key.
  • Each field name is unique
  • Each record is unique.
  • All data is atomic (can't be broken down any futher).

Second Normal Form (2NF):

  • Must be in 1NF
  • All non-key fields can be found using the entire primary key.

Third Normal Form (3NF):

  • Must be in 2NF
  • All non-key fields are fully dependent on the primary key.
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Chapter 5 - Normalisation

Advantages of Normalisation:

  • Removes redunant and duplicate data > Saves storage space
  • Increases Integrity.
  • Increases Consistency
  • Easier Maintenance
  • Flexibility for future expansion.


Disadvantages of Normalisation:

  • Reduces database performance - greater memory/CPU use.
  • Costs time due to lots of editing and deleting of data.
  • Problems with historical calculations.
  • Not appropriate for some types of databases.
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Chapter 5 - Data Dictionary

Data Dictionary - Contains metadata or descriptions of the key items in a database.

It includes:

  • Table Name
  • Field Name
  • Field Data Type
  • Field Length
  • Field Default Value - The value that automatically appears on the creation of a new record.
  • Field Validation
  • Table Security
  • Keys - Primary and foreign keys are identified.
  • Indexes
  • Relationships
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Chapter 5 - Queries

Parameter queries return fields from tables where the value of the parameter is matched.

  • Simple Query - One parameter is searched.
  • Complex Query - More than one parameter is searched.


Complex queries are join together in 3 ways:

  • AND - To include all records found in the queries.
  • OR - To find records that match one or the other searches.
  • NOT - Searches for fields NOT within the parameter.


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Chapter 5 - Queries

Parameters can be static or dynamic:

  • Static Query - Parameters can't be changed so the same parameters are used every time it's run.
  • Dynamic Query - The end user sets the parameters every time the query is run (usually by a dialogue box).
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