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[OBSELETE] AQA - A Level CS > Databases > Flashcards

Databases Flashcards

1
Q

What are serial files

A
  • Data stored in the order in which it was entered
  • No order to the data is maintained
  • Useful for storing transactional data and initialisaion files
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2
Q

What are sequential files?

A
  • Store data in order of a ket field
  • Order is maintained when new records are added
  • Useful for storing master files
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3
Q

What are sequential files?

A
  • Store data in order of a ket field
  • Order is maintained when new records are added
  • Useful for storing master files
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4
Q

What are databases used for?

A
  • Handles large data sets
  • Efficient processing of data
  • Reducing storage requirements
  • Avoiding redundancy
  • Allowing different users to see relevant data
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5
Q

What is the Database Management System (DBMS)

A
  • A manipulation langague to access anmd change the data
  • Integraty to ensure efficiency and structure is not compromised
  • Additional security
  • INterface for other programs to access and use the data
  • Progrma data inderpendence
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6
Q

What are databases made up of?

A
  • Tables that store data in rows and colums
  • Queries to manipulate data: search, sort, add, amend and delete
  • Can create UI and forms
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7
Q

Why is a flat file database bad?

A
  • Only one table
  • Not easy to query
  • Duplicated data + inefficient
  • More errors between datasets = loss of integrety
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8
Q

What do entity relationship models show

A
  • They can show the relationships between databases
  • Can be one to one or one to many
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9
Q

What are primary Keys

A
  • Unique identifier for one record from any other
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10
Q

What is seconday keys?

A
  • Allows for quick ordering of data accoring to a column
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11
Q

What is normalisation?

A
  • Splitting up tables in a database
  • Arranging the data to move it from 1NF to 2NF to 3NF
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12
Q

How do you go from 0NF to 1NF

A
  • Eleminate uplicate columns
  • Get rid of any groups repeating data
  • Identify Primary key
  • Seperate out any attributes which are not atomic into sepearate attributes (One peice of data per field)
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13
Q

How to get from 1NF to 2NF

A
  • Check data is already in 1NF
  • Remove any partial dependencies which is one or more of the attributes depend on only part of the primary key (like course number and student name)
  • Seperate the partial dependencies into different tables
  • Fix any many-to-many relationships found
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14
Q

How do you convert from 2NF to 3NF

A
  • Check data in 2NF
  • Make sure there is no-key dependencies
  • Meaning every field must depend on the primary key
  • If not its seperated again to remove repeating data
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15
Q

What is SQL?

A
  • Allows fast efficient querying
  • Retrieving information from databases
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16
Q

What is the command for deleting data?

A

DELETE from FORM WHERE Forename = ‘9C’

17
Q

What is the command for inserting a new row into the table

A

INSERT INTO Form VALUES (‘10C’, ‘Miss. Badman’, ‘B12’)

18
Q

What is the command for querying a database?

A

SELECT Forename FROM Form WHERE FORM = ‘7R’

19
Q

What is the command for updating an existing command

A

UPDATE Form SET Formteacher = ‘Joey’ WHERE Forename = ‘7R’

20
Q

What is the command for creating a new table?

A

CREATE TABLE Staff(
StaffID INT PRIMARY KEY;
Name VARCHAR(20);
JoinDate date-time;
Age int;
Gender boolean;
)

21
Q

What is transaction processing?

A
  • Any information processing which is divided into individual, indivisible operations
  • Each operation must succeed or fail as a complete unit
22
Q

What transactional statments do all databses have?

A

CRUD
- Create
- Read
- Update
- Delete

23
Q

What does the A.C.I.D rules do?

A

They are a set of rules that ensure data integraty

24
Q

What is atomicity?

A
  • A change to a database must be performed or not performed
  • Any half completed change must not be saved to the datasbe
25
Q

What is consistency?

A

Any change in the databse must retain the overall state of the database

26
Q

What is isolation?

A
  • A transaction must not be able to be interruped by another transaction
  • The transaction must occur in isolation so that other users or processes cannot have access to the data concerned
  • Carried out through record locking where any data used is temporarily put in a read only mode
27
Q

What is durability?

A
  • Once a change has been made to the databse it must not be lost due to a system failure
  • Achived through transactions being stored in secondary storage as soon as possible (as secondary is non volitile)

[OBSELETE] AQA - A Level CS (13 decks)

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