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Databases

Entities, attributes and keys

  • 3 things to know
  • A2 Unit 1

Overview

Term entity, term attribute and term primary key.

What you need to know

Answer each one before you reveal it.

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Key term

What is meant by an entity occurrence?

Key term

Define the term entity.

Key term

Define the term attribute.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Define the term entity.

    Model answer

    An entity is a thing about which a system needs to hold data, such as a customer, an order or a product. Each entity becomes a table in the implemented database.

  2. 2

    Define the term attribute.

    Model answer

    An attribute is a single property of an entity, such as a customer's surname or an order's date. Each attribute becomes a column.

  3. 3

    Define the term primary key.

    Model answer

    A primary key is an attribute, or a combination of attributes, whose value uniquely identifies each record in a table. A primary key may never be duplicated and may never be left empty.

  4. 4

    Define the term composite key.

    Model answer

    A composite key is a primary key made up of two or more attributes together, used where no single attribute is unique. The combination of a student number and a course code identifies one enrolment.

  5. 5

    Define the term foreign key.

    Model answer

    A foreign key is an attribute in one table whose values are the primary key of another table. A foreign key is how a relational database records a relationship between two tables.

  6. 6

    Define the term relationship in a relational database.

    Model answer

    A relationship is an association between two entities that the system must record, such as a customer placing orders. A relationship is implemented by placing the primary key of one table into the other as a foreign key.

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