Fundamentals of Databases Flashcards

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1
Q

Why is normalisation done?

A
  • No redundant data
  • data consistency
  • Make databases more efficient
  • Faster searching and sorting
  • Fewer update/insertion/deletion anomalies
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2
Q

First normal form

A

No repeated groups of attributes / data is atomic

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3
Q

Second normal form

A

No partial key dependencies

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4
Q

Third normal form

A

No non-key dependencies

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5
Q

Define concurrent access

A

When different users attempt to access the same field at the same time

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6
Q

What is the result of concurrent access

A

Data can be lost if 2 users edit a record at the same time

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7
Q

Record Locks

A
  1. User accesses a record
  2. The record is immediately locked
  3. Other users are blocked from accessing it until it is unlocked
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8
Q

Serialisation

A
  1. Requests from the user are put into a queue
  2. Once the first request has been executed, the next is and so on
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9
Q

Time stamp ordering

A
  1. Each command has a timestamp
  2. Commands are carried out in the order of the timestamps
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10
Q

Commitment ordering

A
  1. An algorithm is used to work out an optimum order to execute commands
  2. It takes into account the impacts of them on other parts of the database and prioritises minimisation of issues
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11
Q

Database

A

A persistent, organised store of data (NOT MEMORY)

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12
Q

Explain the concept of a relational database.

A

A relational database stores data in multiple relations that are linked together using relationships. Relations have fields and records.

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13
Q

Entity

A

An object that can be distinguished from other objects. Can be a physical object or a concept. (In a database, this would be a table)

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14
Q

Field / Attribute

A

A characteristic or a feature of an entity. (columns)

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15
Q

Record

A

An instance of an entity. (rows)

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16
Q

Primary Key

A

An attribute that uniquely identifies a record.

17
Q

Composite Primary Key

A

A collection of two or more attributes that uniquely identify a record.

18
Q

Foreign Key

A

The primary key from another table, used to create a link between the tables.

19
Q

What are tables called in relational databases?

A

Tables are called RELATIONS.

20
Q

Format for a primary key

A

Underline.

21
Q

Format for a foreign key

A

Italics or Overline.

22
Q

What two problems do relational databases avoid?

A

Data redundancy and data inconsistency.