1.3.2 Databases Flashcards Preview

A Level Computer Science > 1.3.2 Databases > Flashcards

Flashcards in 1.3.2 Databases Deck (34)
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1
Q

Define a database

A

An organised collection of data

2
Q

Define a table

A

Stores data about a type of entity

3
Q

Define an attribute

A

A column in a table, called a field

4
Q

Define a primary key

A

An entirely unique identifier for an entity

5
Q

Define a composite key

A

A pair of two attributes to make a primary key

6
Q

Define a foreign key

A

A non-primary key attribute in one table which links to the primary key field in another table

7
Q

Define data integrity

A

This refers to the accuracy and reliability of data

8
Q

Define referential integrity

A

This refers to the data integrity in relational databases. It tidies up any effected records.

9
Q

What are the types of entity relationships?

A

1 to 1

1 to many

Many to many

10
Q

Define a flat-file

A

A single table which contains all the data, which can have repeating data or data which extends over multiple lines

11
Q

Define the stages of 1st Normal Form

A
  • Each record has a primary key
  • Data is atomic
  • No repeating groups of attributes
12
Q

Define the stages of 2nd Normal Form

A
  • Data is in 1NF
  • There are no partial dependancies
13
Q

Define the stages of 3rd Normal Form

A
  • Data is in 2NF
  • There are no non-key dependencies
14
Q

What is SQL?

A

The standard tool for working with databases. It is a declarative language

15
Q

Explain the DELETE SQL command

A

DELETE FROM tblName

WHERE [criteria];

This deletes from the table any record which matches the criteria

16
Q

Explain the INSERT SQL command

A

INSERT INTO tblName (field-list)

VALUES (value-list);

This adds a record into the table with the specified values

17
Q

Explain the SELECT SQL command

A

SELECT field-list

FROM tblName

18
Q

Explain the DROP SQL command

A

DROP TABLE tblName

or DROP DATABASE dbName

or DROP INDEX field-name ON tblName

This will delete the item named

19
Q

Explain the JOIN SQL command

A

SELECT field-list

FROM tblName1

JOIN tblName2

On join-criteria

This allows data from 2 different tables to be selected, where the tables are linked with a foreign-primary key pair

20
Q

Explain the ORDER BY SQL command

A

… ORDER BY field1 [ASC/DESC];

This orders the selected data in either ascending or descending order according to the criteria

21
Q

What is the SQL wildcard?

A

*

This states to disregard what comes before/after the * for the given text

22
Q

What is a client-server database?

A

A database residing on a server, with client applications written to access the database

23
Q

What is concurrent requests?

A

When a request is made at the same time as another request

24
Q

What is a problem with concurrent requests?

A

If one request is to update data, while another is to read or update data, then a problem can arise

25
Q

What is a transaction in regards to client-server databases?

A

A single logical action / unit of work

26
Q

What are the features of a good database?

A

Atomicity

Consistency

Isolation

Durability

27
Q

Describe atomicity in regards to databases

A

The components of a transaction are atomic, it must succeed or fail

28
Q

Describe consistency in regards to databases

A

Ensuring an illegal transaction is rejected so that the integrity is upheld

29
Q

Describe isolation in regards to databases

A

Each transaction is dealt with in a way that doesn’t affect others

30
Q

Describe durability in regards to databases

A

Ensuring data is saved once a transaction is completed

31
Q

Define serialisation

A

The concept of multiple transactions executing concurrently with the effect of them executing serially

32
Q

Define record locking

A

The DBMS (Database Management System) will lock an affected record while it is involved in a transaction

33
Q

Define a deadlock in regards to databases

A

When two transactions are trying to access records being used by each other transaction, but both are locked

34
Q

Describe timestamp ordering in regards to databases

A
  • Each record has timestamps for when it was last read and last updated
  • Each transaction has timestamps for when it starts and ends
  • The transactions are carried out in timestamp order
  • The transaction will not go through if the timestamp of a record being updated is after the timestamp of a transaction starting