Unit 4 Exchanging Data

Question 1

What name is given to the public and private keys used in asymmetric encryption?

Answer 1

Key pair

Question 2

Name the two categories of compression

Answer 2

Lossy and lossless

Question 3

In which type of compression is the quality of a file not degraded?

Answer 3

Lossless

Question 4

What is the purpose of encryption?

Answer 4

To keep data secure during transmission

Question 5

Name one type of lossless compression

Answer 5

One from:
● Run length encoding
● Dictionary encoding

Question 6

In which form of encryption do the sender and receiver share the same private key?

Answer 6

Symmetric encryption

Question 7

How many keys are used in asymmetric encryption?

Answer 7

Two (one public and one private)

Question 8

If person A wants to send a message to person B using asymmetric encryption, which key should they use to encrypt the message?

Answer 8

B’s public key

A message encrypted with B’s public key can only be decrypted with B’s private key, which only B has access to

Question 9

What is said to have occured when two keys map to the same hash?

Answer 9

A collision

Question 10

In which kind of lossless compression are repeated characters replaced by one occurrence and the number of times to repeat the character?

Answer 10

Run length encoding

Question 11

What name is given to the process of turning an input into a fixed size value?

Answer 11

Hashing

Question 12

Which data structure uses hashing to store information with constant lookup time?

Answer 12

Hash table

Question 13

What is meant by compression?

Answer 13

The process of reducing the space required to store a file

Question 14

Name two properties that a hashing algorithm should have

Answer 14

● Low chance of collision
● Quick to calculate
● Output smaller than input

Question 15

Lossy compression

Answer 15

Lossy compression​ reduces the size of a file ​while also​ removing some of its information​. This could result in a ​more pixelated​ image or​ less clear​ audio recording.

Question 16

Lossless compression​

Answer 16

Lossless compression​, the original file ​can be recovered ​from the compressed version. Something which is​ not possible​ when using lossy compression which reduces the size of the file by ​completely disregarding​ some information.

Question 17

Run Length Encoding

Answer 17

Run length encoding is a ​method of lossless compression​ in which repeated values are removed and replaced with ​one occurrence​ of the data followed by the ​number of times​ it should be repeated.

Question 18

What would the string AAAAAABBBBBCCC be represented as

Answer 18

A6B5C3

Question 19

Dictionary encoding

Answer 19

Dictionary encoding is another example of a method of​ lossless compression​. Frequently occurring pieces of data are replaced with an index and compressed data is stored alongside a ​dictionary ​which matches the frequently occurring data to an index. The original data can then be restored using the dictionary.

Question 20

Encryption

Answer 20

Encryption is used to​ keep data secure​ when it’s being transmitted.

Question 21

Symmetric Encryption

Answer 21

In symmetric encryption, both the sender and receiver share the same​ private key​, which they distribute to each other in a process called a ​key exchange​. This key is used for both encrypting and decrypting​ data.
It’s important that the private key is kept ​secret​. If the key is intercepted during the key exchange then any communications sent can be intercepted and decrypted using the key. Asymmetric encryption gets around this issue.

Question 22

Asymmetric Encryption

Answer 22

When sending information using asymmetric encryption,​ two keys ​are used: one public and a second, private, key. The public key can be published ​anywhere​, free for the world to see, while the private key must be kept secret. Together, these keys are known as a​ key pair ​and are ​mathematically related ​to one another.

Question 23

Hashing

Answer 23

Hashing is the name given to a process in which an input (called a key) is turned into a fixed size value (called a hash).

Question 24

Relational Databases

Answer 24

Relational database work by splitting data about different entities (types of things) into separate relations (tables). Each relation only contains data about one entity and relationships (connections) are made between each of the relations through the use of primary and foreign keys.

Question 25

Flat File

Answer 25

A flat file is a database that consists of a ​single file​. The flat file will most likely be based around a ​single entity and its attributes​. Flat files are typically written out in the following way: Entity1​(​Attribute1​, Attribute2, Attribute3 ...)

Question 26

Primary Key

Answer 26

A primary key is a ​unique identifier​ for each ​record ​in the table.

Question 27

Foreign Key

Answer 27

A foreign key is the attribute which ​links two tables together​. The foreign key will exist in one table as the primary key and act as the foreign key in another.

Question 28

Secondary Key

Answer 28

A secondary key allows a database to be​ searched quickly​. The patient is unlikely to remember their patientID but will know their surname. Therefore, a secondary index ​(secondary key) is set up on the surname attribute. This makes it possible to ​order and search ​by surname which makes it easier to find specific patients in the database.

Question 29

One-to-one​

Answer 29

Each entity can only be linked to one other entity, such as the relationship between a husband and wife. The husband entity can only be associated with one wife entity and vice versa.

Question 30

One-to-many​

Answer 30

One table can be associated with many other tables, such as a mother having multiple children. Similarly, multiple child entities can be linked to the same mother entity.

Question 31

Many-to-many​

Answer 31

One entity can be associated with many other entities and the same applies the other way round. An example is students and courses - each student can enrol in more than one course and each course can have more than one student.

Question 32

Normalisation

Answer 32

The process of coming up with the ​best possible layout​ for a ​relational database​ is called normalisation. Normalisation tries to accomplish the following things: ● No redundancy​ (unnecessary duplicates). ● Consistent data​ throughout linked tables. ● Records can be​ added and removed without issues. ● Complex ​queries ​can be carried out.

Question 33

First Normal Form

Answer 33

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

Question 34

Second Normal Form

Answer 34

A database which ​doesn’t have any partial dependencies​ and is in​ first normal form​ can be said to be in second normal form. This means that no attributes can depend on part of a composite key.

Question 35

Third Normal Form

Answer 35

If the database is in ​second normal form​ and contains ​no non-key dependencies,​ it is in third normal form. A non-key dependency means the attribute only depends on the value of the primary key and nothing else.

Question 36

Indexing

Answer 36

Indexing is a ​method​ used to store the position of each record ordered by a certain attribute. This is used to look up and access data quickly. The ​primary key​ is ​automatically indexed​; however, the primary key is almost never queried since it is not normally remembered. This is why secondary keys are used. Secondary keys are indexed to make the table easier and faster to search through on those particular attributes.

Question 37

Capturing Data

Answer 37

Data needs to be input into the database and there are multiple methods of doing this. The chosen method is always dependent on the context. For example, if pedestrians are participating in a survey, their responses will need to be ​manually entered​ into the database. Data is also captured when people pay cheques. Banks scan cheques using ​Magnetic Ink Character Recognition (MICR)​. All of the details excluding the amount are printed in a special magnetic ink which can be recognised by a computer but the amount must be entered manually. ​Optical Mark Recognition (OMR)​ is used for multiple choice questions on a test. Other forms use​ Optical Character Recognition (OCR)

Question 38

SQL

Answer 38

SQL stands for ​Structured Query Language​ and is a declarative language​ used to ​manipulate databases​. SQL enables the creating, removing and updating of databases.

Question 39

SELECT, FROM, WHERE

Answer 39

The ​SELECT​ statement is used to ​collect fields from a given table​ and can be paired with the ​FROM​ statement to ​specify which table(s) the information will come from​. The ​WHERE statement can be used in conjunction to specify the search criteria.

Question 40

ORDER BY

Answer 40

The​ ORDER BY ​part of the code specifies whether you want it in ​ascending or descending order. Values are automatically placed in ascending order and adding ‘Desc’ to the end of statement will cause values to be displayed in descending order: ORDER BY DatePublished Desc

Question 41

JOIN

Answer 41

JOIN​ provides a method of ​combining rows from multiple tables​ based on a ​common field between them. The example below shows the joining of two tables, Movies and Directors.

Question 42

CREATE

Answer 42

The ​CREATE​ function allows you to ​make new databases​, as shown below: CREATE TABLE TableName

Question 43

Data Types

Answer 43

- CHAR(n)​: this is a string of fixed length n - VARCHAR(n)​: this is a string of variable length with upper limit n - BOOLEAN​: TRUE or FALSE values - INTEGER/INT​: integer - FLOAT​: number with a floating decimal point - DATE​: the date in the format Day/Month/Year - TIME​: the time in the format Hour/Minute/Second - CURRENCY​: sets the number as a monetary amount

Question 44

Transaction Processing

Answer 44

A transaction is defined as a ​single operation executed on data​. However a collection of operations can also sometimes be considered a transaction.

Question 45

ACID

Answer 45

Atomicity, Consistency, Isolation, Durability

Question 46

Atomicity

Answer 46

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

Question 47

Consistency

Answer 47

Ensures that no transaction can violate any of the defined validation rules for maintaining the integrity of the database. When a database is created, referential integrity rules will be specified between linked tables.

Question 48

Isolation

Answer 48

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

Question 49

Durability

Answer 49

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.

Question 50

Record Locking

Answer 50

The process of ​preventing simultaneous access to records​ in a database is called record locking and it is used in order to ​prevent inconsistencies​ or a ​loss of updates​. While one person is editing a record, this ‘locks’ the record so prevents others from accessing the same record.

Question 51

Redundancy

Answer 51

Some information is very important and people and companies cannot afford to lose this information. This is where redundancy comes in. Redundancy is the process of having one or more copies of the data in ​physically different locations​. This means that if there is any damage to one copy the others will remain unaffected and can be recovered