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Computer Science > Section 11 - Databases and Normalisation > Flashcards

Section 11 - Databases and Normalisation Flashcards

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1
Q

What is an entity?

A

A category of object, person, event or thing of interest to a organisation about which data is to be recorded

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2
Q

What does every entity in a database have?

A

Attributes

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3
Q

What are attributes?

A

Details of an entity

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4
Q

How are attributes listed?

A

Inside the brackets

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5
Q

What is a primary key?

A

A unique identifier for each record in a table

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6
Q

How is a primary key shown?

A

It is underlined

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7
Q

What are the 3 types of entity/table relationships?

A

One-to-one
One-to-many
Many-to-many

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8
Q

What is a one-to-one relationship?

A

Where each entity can only be linked to one other entity

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9
Q

What is a one-to-many relationship?

A

One table can be associated with many other tables

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10
Q

What is a many-to-many relationship?

A

One entity can be associated with many other entities, and vice versa

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11
Q

How are one-to-one relationships displayed?

A

A single line connecting the 2 entities

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12
Q

How are one-to many relationships displayed?

A

The line will have a branch on one side (the many side)

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13
Q

How are many-to-many relationships displayed?

A

There will be branches on both sides of the line

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14
Q

What is a relational database?

A

A collection of tables in which relationships are modelled by shared attributes

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15
Q

What is a foreign key?

A

A unique identifier that links 2 tables together. In one table the key will exist as the primary key, whilst in another table it will exist as a foreign key

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16
Q

What is a composite primary key?

A

A primary key that consists of more than one attribute

17
Q

What is a secondary key?

A

A unique identifier that allows a database to be searched quickly.

18
Q

How can a record with a particular primary key be found quickly?

A

The database will automatically maintain an index of primary keys, giving the position of their respective records

19
Q

What is normalisation?

A

The process of designing the best possible layout for a relational database

20
Q

What does normalisation attempt to accomplish?

A
  • No redundancy
  • Consistent data throughout the linked tables
  • Records can be added and removed without issues
  • Complex queries can be carried out
21
Q

What is first normal form?

A

A table is in 1NF if each attribute is atomic with no repeating attribute

22
Q

What is the definition of atomic?

A

Containing a single value

23
Q

What is a relation?

A

A table in a relational database

24
Q

When is a link table needed?

A

Whenever 2 entities have a many-to-many relationship

25
Q

What is second normal form?

A

A table is in 2NF if it is in 1NF and it contains no partial dependencies

26
Q

What is a partial dependency?

A

When one or more attributes depend on only part of the primary key

27
Q

What does partial dependency occur?

A

When the primary key is a composite key

28
Q

What is third normal form?

A

A table is in 3NF if it is in 2NF and all attributes are dependant on the key, the whole key, and nothing but the key

29
Q

What are the advantages of normalisation?

A
  • Maintaining and modifying the database
  • Faster sorting and searching
  • Deleting records
30
Q

How is a normalised database easier to maintain and modify?

A
  • Data integrity is maintained because there is no unnecessary duplication of data. This means that when an attribute needs updating, it only needs to be changed in a single position
31
Q

How is a normalised database faster to sort and search?

A

A normalised database produces smaller tables with fewer fields, meaning there is less data and operations are quicker

32
Q

How is a normalised database advantageous for deleting records?

A

If set up correctly, a normalised database will not allow records in a table on the ‘one’ side of a one-to-many relationship to be deleted accidently

Computer Science (13 decks)

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