Data Exchange (unit 4) (finished)

Question 1

Lossy Compression

Answer 1

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.

Question 2

Lossless Compression

Answer 2

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.

Question 3

Run Length Encoding

Answer 3

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.

Question 4

Dictionary Coding

Answer 4

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.

Question 5

Purpose of Compression

Answer 5

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

Question 6

uses of lossy

Answer 6

multimedia files e.g. MP3, JPEG, MPEG

Question 7

uses of lossless

Answer 7

text files and computer programs

Question 8

Encryption

Answer 8

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

Question 9

Symmetric Encryption

Answer 9

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.

Question 10

Negatives of Symmetric encryption

Answer 10

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.

Question 11

Asymmetric Encryption

Answer 11

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

Question 12

Hashing

Answer 12

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.

Question 13

Uses of Hashing

Answer 13

• generating disk address

- storing and checking passwords

Question 14

digital signature

Answer 14

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

Question 15

Uses of assymetric encryption

Answer 15

used for transfering data e.g. online shopping

Question 16

Uses of symmetric encryption

Answer 16

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

Question 17

benefits of symmetric

Answer 17

• encrypted very quickly

- simple and easy

Question 18

Benefits of asymmetric

Answer 18

• no movement of keys, more secure

- can be used for digital signatures

Question 19

drawbacks of assymmetric

Answer 19

• not as fast

Question 20

Database

Answer 20

Databases are structured, persistent collections of data.

Question 21

Flat File

Answer 21

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

Question 22

Relational Database

Answer 22

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.

Question 23

Entity Relationship Modelling

Answer 23

when the relationships between tables are shown in abstracted view.

Question 24

relationships

Answer 24

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

Question 25

primary key

Answer 25

A field that uniquely identifies each record

Question 26

Foreign key

Answer 26

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

Question 27

composite key

Answer 27

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

Question 28

Secondary key

Answer 28

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

Question 29

Method of capturing data (Automated)

Answer 29

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

Question 30

Method of capturing data (Manual)

Answer 30

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

Question 31

Data redundancy

Answer 31

The unnecessary duplication of data in a database

Question 32

Variable length fields

Answer 32

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

Question 33

Hashing Databases

Answer 33

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

Question 34

Attribute/field

Answer 34

the columns (describes the characteristics of each record)

Question 35

Record/Tuple

Answer 35

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

Question 36

Normalisation

Answer 36

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

Question 37

Atomic

Answer 37

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

Question 38

partial key dependency

Answer 38

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

Question 39

non key dependency

Answer 39

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

Question 40

all attributes are dependent on..

Answer 40

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

Question 41

first normal form

Answer 41

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

Question 42

second normal form

Answer 42

1. It is in first normal form.
2. It does not have any non-prime attribute that is functionally dependent on any proper subset of any candidate key of the relation. A non-prime attribute of a relation is an attribute that is not a part of any candidate key of the relation.

Question 43

third normal form

Answer 43

1. In second normal form

2. if there is no transitive dependency for non-prime attributes

Question 44

SQL

Answer 44

Structured Query Language, used to manage relational databases

Question 45

create a new table SQL

Answer 45

CEATE TABLE (table name)

Question 46

Insert data into a table SQL

Answer 46

INSERT INTO (table) (column1, column2, column3...)
VALUES (value1, value2, value3...)

Question 47

Query SQL

Answer 47

SELECT column1, column2, …

FROM table_name;

Question 48

Order Queried data SQL

Answer 48

SELECT column1, column2, …
FROM table_name
ORDER BY column1, column2, … ASC|DESC;

Question 49

update attribute SQL

Answer 49

UPDATE table_name
SET column1 = value1, column2 = value2, …
WHERE condition;

Question 50

Condition between two values SQL

Answer 50

SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

Question 51

Check if an attribute is similar to a given value SQL

Answer 51

SELECT column1, column2, …
FROM table_name
WHERE columnN LIKE pattern;

Question 52

Data Integrity

Answer 52

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

Question 53

Referential Integrity

Answer 53

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.

Question 54

Transaction Processing

Answer 54

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

Question 55

ACID

Answer 55

Atomicity
Consistency
Isolation
Durability

Question 56

Atomicity

Answer 56

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.

Question 57

Consistency

Answer 57

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

Question 58

Isolation

Answer 58

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.

Question 59

Durability

Answer 59

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