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IT > Normalisation > Flashcards

Normalisation Flashcards

1
Q

What is a relational database

A

When there is multiple tables in a database that relate to each other

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2
Q

What is a table

A

A collection of records

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3
Q

What is a record

A

A collection of fields

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4
Q

What is a field

A

An column that stores a single data item

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5
Q

What is a relation

A

A table

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6
Q

What manages relational databases

A

The DataBase Management Systems (DBMS)

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7
Q

What is a primary key

A

A field in a table that uniquely identifies each record in the table. No values in the primary key fields are repeated

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8
Q

What is a super key

A

A combination of fields in a table which uniquely identifies each row.

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9
Q

What are candidate keys

A

Minimal super keys. In other words there must be no attributes included in that do not contribute to the uniqueness of the rows. They are the possible options for the primary key

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10
Q

What are the three types of keys

A

Super keys, candidaté keys, primary keys

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11
Q

What is a composite key

A

A combination of two or more fields to form a primary key.

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12
Q

Which is more serious deleting a record or an attribute ?

A

Deleting a record is removing an entire row of data whereas deleting an attribute is deleting an entire column. The seriousness depends on the data

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13
Q

What is a database schema

A

When there is multiple tables in a database that relate to each other

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14
Q

What does normalisation avoid

A
  • Repeating groups
  • Data redundancy
  • Anomalies - update, insertion, and deletion
  • complex queries
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15
Q

What are repeating groups

A

A field that can have multiple values

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16
Q

What is data redundancy

A

When the primary key is expanded

17
Q

What is an update anomaly

A

When the same data needs to be updated in more than one place

18
Q

What is an insertion anomaly

A

When records are added that do that satisfy the primary key requirements

19
Q

What is a deletion anomaly

A

When a deletion. Share unnecessary loss of data

20
Q

What is normalisation

A

The process of diving a set of data into smaller tables using a defined set of rules

21
Q

What are the characteristics of 1NF

A

No repeating groups
Choose a primary key

22
Q

What are the characteristics of 2NF

A

Relation is in 1NF
No partial dependencies

23
Q

What are the characteristics of 3NF

A

Relation is in 2NF
No transitive dependencies

24
Q

What is a dependency

A

When one field is related to another.

25
Q

What is a partial dependency

A

When a fields value is dependent on only part of a composite key

26
Q

What is a transitive dependency

A

When a fields value is dependent on a non-primary key field

27
Q

What is derived data

A

When you use a field to calculate another. Derived data is not stored

28
Q

What is duplicate data

A

When a record has the same value for a field of another record.

29
Q

What is the difference between duplicate data and data redundancy

A

Data redundancy is produced by repeating groups in the first normal form hence it must be removed to normalise the table whereas duplicate data is not wrong must not be removed. Eg two students living in the same road

30
Q

What is atomic data

A

When each value of a field stores a single data item.

31
Q

What is the difference between dependency and derived data

A

Dependency does not involve calculation but rather is a relationship between two fields whereas derived data is calculated from another field and is not stored.

32
Q

What is a foreign key

A

A field in a table that is a primary key in another table

33
Q

What is referential integrity do

A

It prevent the insertion of a data that refers to other data that doesn’t exist and the removal of data that relates to other data

34
Q

What does a one to one relationship entail

A

Both fields are put in the same table

IT (8 decks)

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