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A-Level Computer Science OCR LTS > Exchanging Data > Flashcards

Exchanging Data Flashcards

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1
Q

Lossy Compression

A

Actual data is removed from the file in order to reduce its size. An algorithm is used to strip out the least important data. The original file cannot be restored as data is physically removed.

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2
Q

Lossless Compression

A

Reduces the file size but allows the original data be perfectly reconstructed from the compressed data. Actual data is still removed however the data is encoded in such a way that the original can be recreated.
Less effect at reducing file size than lossy.

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3
Q

Run Length Encoding

A

Run length encoding is used when there is repeated redundant data. It stores the item once and then an index with how often the item is repeated.

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4
Q

Dictionary Coding

A

Dictionary coding is when an index is built where every data item in the file is recorded along with an indexed reference. The final compressed file will just consist of the dictionary index along with the sequence of occurrences needed to recreate the original file.

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5
Q

Purpose of Compression

A
  1. Reduce download times
  2. Reduce requirements on file storage
  3. Make best use of bandwidth
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6
Q

uses of lossy

A

multimedia files e.g. MP3, JPEG, MPEG

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7
Q

uses of lossless

A

text files and computer programs

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8
Q

Encryption

A

Encryption is the process of encoding a message so that it can be read only by the sender and the intended recipient.

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9
Q

Symmetric Encryption

A

Symmetric Encryption is when the same key is used to encrypt and decrypt the message. Both party’s must know the key and also keep it secret.

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10
Q

Negatives of Symmetric encryption

A

There is a security risk as the key may be intercepted or the process of creating the key may be duplicated meaning the data can be decrypted by a third party.

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11
Q

Asymmetric Encryption

A

Asymmetric Encryption (Public Key Cryptography) is when a public key and a private key is used. The public key is used to encrypt the data and the private key is used to decrypt the data. If you use person X’s public key to encrypt the data only person X’s private key will be able to decrypt it

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12
Q

Hashing

A

Hashing is the process used to transform a data item into something different. A hashing function provides a mapping between an arbitrary length input and a fixed length output. It is a one-way transformation meaning you cannot get back to the original form.

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13
Q

Uses of Hashing

A
  • generating disk address

- storing and checking passwords

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14
Q

digital signature

A

hash total is encrypted using the users private key. If the receiver can decryptit using the senders public key they know that the message is authentic

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15
Q

Uses of assymetric encryption

A

used for transfering data e.g. online shopping

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16
Q

Uses of symmetric encryption

A

Used when the same person is accessing and saving data e.g. for backing up

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17
Q

benefits of symmetric

A
  • encrypted very quickly

- simple and easy

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18
Q

Benefits of asymmetric

A
  • no movement of keys, more secure

- can be used for digital signatures

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19
Q

drawbacks of assymmetric

A
  • not as fast
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20
Q

Database

A

Databases are structured, persistent collections of data.

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21
Q

Flat File

A

single table database. It is inefficient as it is difficult to query and leads to data redundancy which can cause errors.

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22
Q

Relational Database

A

A relational database has more than one related table. It is more efficient that a flat file database as no data is duplicated meaning querying is easier.

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23
Q

Entity Relationship Modelling

A

when the relationships between tables are shown in abstracted view.

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24
Q

relationships

A

one-to-one
one-to-many
many-to-many

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25
Q

primary key

A

A field that uniquely identifies each record

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26
Q

Foreign key

A

a foreign key is a field in one table that uniquely identifies a row of another table

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27
Q

composite key

A

A composite key is a combination of two or more columns in a table that can be used to uniquely identify a row.

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28
Q

Secondary key

A

any field in a database which is not a primary, candidate or foreign key. They are used to order queries.

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29
Q

Method of capturing data (Automated)

A

barcode readers, scanners, sensors, magnetic ink character recognition, smart card readers

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30
Q

Method of capturing data (Manual)

A

Paper data capture form (read by OCR & OMR or typed in manually)

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31
Q

Data redundancy

A

The unnecessary duplication of data in a database

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32
Q

Variable length fields

A

an element may use a different number of bytes to another element for example a different number of characters.
Means it only uses the necessary amount of storage

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33
Q

Hashing Databases

A

transforms a string of characters in a record into a shortened form that can be used as a disk address

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34
Q

Attribute/field

A

the columns (describes the characteristics of each record)

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35
Q

Record/Tuple

A

the rows (a data set that applies to one item)

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36
Q

Normalisation

A

Organising the attributes and relations of a relational database to minimise redundancy

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37
Q

Atomic

A

data is in its lowest level of detail and cannot be split into separate attributes

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38
Q

partial key dependency

A

one or more f the attributes depends on only part of the primary key (if the primary key is a composite key)

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39
Q

non key dependency

A

where the value of an attribute is determined by the value of another attribute which is not part of the key.

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40
Q

all attributes are dependent on..

A

the key, the whole key, and nothing but the key

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41
Q

first normal form

A
  1. Eliminate duplicate columns
  2. Get rid of any groups of repeating data
  3. Identify the primary key
  4. Separate out any attributes which are not atomic into separate attributes
42
Q

second normal form

A
  1. Check the data is already in 1NF
  2. Remove any partial dependencies
  3. ‘fix’ any many to many relationships you discover
43
Q

third normal form

A
  1. Check the data is already in 2NF

2. Check there are no non-key-dependencies

44
Q

SQL

A

SQL is a language which allows for fast, efficient querying and reporting of vast amounts of data held in a relational database. It is a very high-level language.

45
Q

create a new table SQL

A

CREATE TABLE tblName

46
Q

Insert data into a table SQL

A

INSERT INTO tblName

47
Q

Query SQL

A

SELECT *
FROM tblName
WHERE conditions

48
Q

Order Queried data SQL

A

ORDER BY

49
Q

update attribute SQL

A

SET

50
Q

Condition between two values SQL

A

WHERE x BETWEEN a AND b

51
Q

Check if an attribute is similar to a given value SQL

A

LIKE

52
Q

Data Integrity

A

Data integrity is the maintenance and consistency of data in a data store.
The data store must reflect the reality that it represents.

53
Q

Referential Integrity

A

Referential Integrity is where table relationships must always be consistent.
Any foreign key field must agree with the primary key that is referenced by the foreign key. Thus, any changes to the primary key field must be applied to all foreign keys in another table, or not at all.

54
Q

Transaction Processing

A

any information processing which is divided into individual, indivisible operations each operation must secede or fail as a complete unit.

55
Q

ACID

A

Atomicity
Consistency
Isolation
Durability

56
Q

Atomicity

A

a change to a database is either completely performed or not performed at all. A half-completed change MUST NOT be saved back to the database.

57
Q

Consistency

A

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

58
Q

Isolation

A

a transaction must not be able to be interrupted by anther transaction. The transaction must occur in isolation so that other users or processes cannot have access to the data concerned.

59
Q

Durability

A

Once a change has been made to a database it must not be lost due to a system failure.

60
Q

Record Locking

A

Recording Locking prevents simultaneous access to objects in a database in order to prevent updates being lost or inconsistencies in the data arising.

61
Q

Database Management System

A

software that handles the data that is stored in secondary storage.

62
Q

What does the DMBS provide

A 
Security
backups
index updating
enforcement of referential integrity
facilities to update and query the database
63
Q

Why Do RISC processors result in increased battery life

A
  • smaller instruction set
  • fewer transistors/ less complex circuitry
  • less power required
64
Q

Composite Key

A

A unique identifier made from different fields

65
Q

Secondary Key

A

Any field which isn’t a primary/composite key which can help make a query more efficient

66
Q

Methods of sending data

A
  • Electronic Data Interchange (EDI)
  • Application Programming Interface (API)
  • A URL to a file
67
Q

EDI

A

Is the computer-to-computer exchange of business documents in a standard electronic format between business partners.

68
Q

API

A

a prewritten set of subroutines that provide access to the

companies data

69
Q

Formats of data

A
  • CSV (Comma Separated Value)
  • XML (eXstensible Markup Language)
  • SQL (Structured Query Language)
70
Q

CSV (Comma Separated Value)

A

A text file/format with values separated by

commas

71
Q

XML (eXstensible Markup Language)

A

A markup language that uses tags to denote data

72
Q

SQL (Structured Query Language)

A

A language for creating/querying databases

73
Q

SQL query

A

SELECT
FROM
WHERE

74
Q

SQL similar elements

A

LIKE

75
Q

delete rows of a table

A

DELETE
FROM
WHERE

76
Q

insert items into a table

A

INSERT INTO table_name (column….)

VALUES (value…)

77
Q

delete full tables SQL

A

DROP TABLE table_name;

78
Q

combine rows from multiple rows

A

JOIN

79
Q

wildcard

A

*, selects all the elements

80
Q

positives of the DBMS?

A
  • provide security
  • provide automatic backup
  • enforce data integrity rules
  • control data redundancy
  • provide users with controlled access to data they need
81
Q

what does security keeping data safe from?

A
  • accidental or deliberate loss

- malicious access

82
Q

Data integrity is the state of data being

A

as intended and accurate

83
Q

persistent

A

the data remains for as long as its required

84
Q

structured

A

the data is organised in a logical way

85
Q

indexing

A

used to quickly access and locate data in a table

86
Q

Data redundancy

A

the unnecessary duplication of data in a database. When updates occur, all the instances of a data item must be changed. This leads to errors and also wastes storage space.

87
Q

relational databases

A

multiple tables linked together

88
Q

deadlock

A

when both users try and access the database at the exact same time meaning neither can edit it

89
Q

Timestamp ordering

A

every object has a read timestamp and a write timestamp meaning if the read timestamps are not the same the DBMS knows another user has accessed the same object

90
Q

how is redundancy used usefully

A

organisations build in redundancy e.g. duplicate hardware so that if the main system fails the backup can take over

91
Q

Two characteristics to look for in a hashing algorithm

A
  • quick to calculate
  • minimizes the collisions
  • provides a smaller output than input
92
Q

EDI

A

Electronic data interchange is the computer to computer exchange of documents. All documents must be in a standard format/

93
Q

Serialisation techniques

A

Timestamp ordering

Commitment ordering

94
Q

Serialisation

A

The process of ensuring transactions do not overlap in time and therefore cannot interfere with each other

95
Q

why is removing many-to-many relationships good?

A
  • takes the table to 3NF

- reduces data inconsistencies/ redundancies

96
Q

Uses of sequential files

A

address/ telephone books

97
Q

Uses of serial files

A

storing transactions of a shop

98
Q

structured

A

Data arranged in a logical and consistent pattern

99
Q

Benefits of fixed length fields

A
  • easier to write the software
  • easier to search
  • file size can be estimated or planned
100
Q

what order are records stored in a database

A

no order, whichever order they’re inputted

101
Q

Why are primary keys neccessary?

A
  • to identify a row unambiguously

- To link to the foreign keys of other tables

102
Q

Difference between data redundancy and data integrity

A
  • Data redundancy is unnecessary repetition of data

- Data integrity is accurate data which reflects reality

A-Level Computer Science OCR LTS (15 decks)

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