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NSFC A Level Computer Science > 1.3.2 - Databases > Flashcards

1.3.2 - Databases Flashcards

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1
Q

What is an entity?

A

An item of interest about which information is stored.

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2
Q

What is a relational database?

A

A set of tables whose records are linked by certain fields.

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3
Q

What is a flat-file database?

A

A flat-file database is a database that consists of a single file. It is usually based on a single entity.

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4
Q

How is a flat-file database written?

A

Entity(Attribute1, Attribute2, Attribute3)

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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 the primary key shown?

A

It is underlined.

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7
Q

What is a foreign key?

A

An attribute that links two tables together.

The foreign key exists in one table as the primary key and acts as the foreign key in another.

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8
Q

What is a secondary key?

A

A non-unique but specific identifier that allows data to be searched easier.

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9
Q

What is the advantage of using a secondary key?

A

It allows for the database to be searched easier. For example, a patient will probably not know their patient ID but will know their surname.

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10
Q

What are the three types of entity relationships?

A

One-to-one

One-to-many

Many-to-many.

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11
Q

What is the main feature of a one-to-one entity-relationship?

A

One entity can be linked to only one other entity.

For example, the relationship between a husband and wife.

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12
Q

What is the main feature of a one-to-many entity relationship?

A

One entity can be associated with many other entities.

For example, a mother having multiple children.

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13
Q

What is the main feature of a many-to-many entity relationship?

A

Multiple entities can be linked to multiple entities.

For example, the relationship between students and courses.

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14
Q

What is normalisation?

A

The process of coming up with the best possible layout for a relational database.

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15
Q

What does normalisation try to achieve?

A

No redundancy.

Consistent data throughout linked tables.

Complex queries can be carried out.

Records can be added and removed without issues.

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16
Q

What are the three types of normalisation?

A

First normal form (1NF)

Second normal form (2NF)

Third normal form (3NF).

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17
Q

What are the conditions for first normal form?

A

There must be no attribute that contains more than a single value.

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18
Q

What are the conditions for second normal form?

A

It must be in first normal form.

The database must not have any partial key dependencies - no attributes depend on a composite key.

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19
Q

What are the conditions for third normal form?

A

It must be in second normal form.

There must not be any non-key dependencies - the attribute only depends on the value of the primary key.

20
Q

Name two ways data is captured.

A

Manual entering.

Magnetic ink character recognition.

Optical mark recognition.

Optical character recognition.

21
Q

What does EDI stand for?

A

Electronic data interchange.

22
Q

What does the ‘SELECT’ syntax do in SQL?

A

It collects fields from a given table.

23
Q

What does the ‘FROM’ syntax do in SQL?

A

It specifies which table the information comes from.

24
Q

What does the ‘WHERE’ syntax do in SQL?

A

It is used to specify the search criteria.

25
Q

What does the ‘ORDER BY’ syntax do in SQL?

A

It specifies whether the data is outputted in ascending or descending order.

26
Q

What does the ‘JOIN’ syntax do in SQL?

A

It provides a method of combining rows from multiple tables based on a common field.

27
Q

What does the ‘CREATE’ syntax do in SQL?

A

Allows new databases to be created.

28
Q

What does the ‘ALTER’ syntax do in SQL?

A

Adds, deletes or modifies the columns in a table.

29
Q

What does the ‘INSERT INTO’ syntax do in SQL?

A

Inserts a new record into a database table.

30
Q

What does the ‘UPDATE’ syntax do in SQL?

A

Used to update a record in a database table.

31
Q

What does the ‘DELETE’ syntax do in SQL?

A

Used to delete a record from a database table.

32
Q

What is the syntax for the ‘CREATE’ function?

A

CREATE TABLE tableName
(
Attribute1 INTEGER NOT NULL, PRIMARY KEY
Attribute2 VARCHAR(20) NOT NULL,
…
)

33
Q

What is the syntax for the ‘ALTER’ function?

A

ALTER TABLE tableName

MODIFY COLUMN AttributeX NewDataType

34
Q

What is the syntax for the ‘UPDATE’ function?

A

UPDATE tableName
SET column1 = value1, column2 = value2
WHERE columnX = value

35
Q

What is the syntax for the ‘DELETE’ function?

A

DELETE FROM tableName

WHERE columnX = value

36
Q

What is referential integrity?

A

Referential integrity is the process of ensuring consistency. This ensures that information is not used if it is required elsewhere in a linked database.

37
Q

What is a transaction?

A

A transaction is defined as a single operation executed on data.

38
Q

What does ACID stand for?

A

Atomicity, Consistency, Isolation, Durability.

39
Q

What does atomicity mean?

A

A transaction must be processed in its entirety or not at all.

40
Q

What does consistency mean?

A

A transaction must maintain the referential integrity rules between linked tables.

41
Q

What does isolation mean?

A

Simultaneous executions of transactions should lead to the same result as if they were executed one after the other.

42
Q

What does durability mean?

A

Once a transaction has been executed it will remain so regardless of the circumstances surrounding it, such as in the event of a power cut.

43
Q

What is record locking?

A

The process of preventing simultaneous access to records in a database.

44
Q

What is deadlock?

A

When two records are locked due to them being processed but the records depend on each other for the transaction.

45
Q

What is redundancy?

A

The process of having one or more copies of the data in physically different locations.

NSFC A Level Computer Science (26 decks)

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