Exchanging Data 1.3 Flashcards
Name the two categories of compression
Lossy and lossless
Explain lossless compression
lossless compression reduces the size of a file without losing any information
The original file can be recovered from the compressed
version
Explain lossy compression
lossy compression reduces the size of a file while also removing some of its information
What is the purpose of encryption?
To keep data secure during transmission
Name types of lossless compression
- Run Length Encoding
- Dictionary Encoding
Explain Run Length Encoding (RLE)
RLE 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
For example, the string AAAAAABBBBBCCC could be represented as A6B5C3 since ‘A’ is repeated 6 times etc..
When would and wouldnt you use run length encoding?
You would use run length encoding if there are many consecutive values. if there arent many it would not be useful
Explain Dictionary Encoding
Frequently occurring pieces of data are replaced with an index and compressed data is stored in a dictionary
The original data can then be restored using the dictionary.
When would dictionary encoding be used?
passages with repeated phrases
What is symmetric encryption?
Both the sender and receiver share the same private, This key is used for both
encrypting and decrypting data
If the key is intercepted during the key
exchange then any communications sent can be intercepted and decrypted using the key.
What is asymmetric encryption?
Both parties have a public and private key, where the public key is used for encryption and the private key is used for decryption
If person A wants to send a message to person B using asymmetric encryption, what key should they use to encrypt the message?
Person B’s public key
A message encrypted with B’s public key can only be decrypted with B’s private key which only person B has access to
What is it meant by compression?
Compression is the process of reducing the space requires to store a file
What is Hashing?
A technique used to store and retreive data in a table by using a unique key. it is used ti speed up searches and comparisions
Name two properties that a hashing algorithm should have
- Low chance of collision
- Quick to calculate
- Output smaller than the input
What is a Relational database?
a relational database is a type of database that stores data in tables, which are related through common fields
What is an entity?
An item of interest about which information is stored
what is a flat file?
A database that consists of a single file usually about one entity
What is a primary key?
A unique identifier for each record in a table
What is a foreign key?
The attribute which links two tables together
What is a secondary key and what is it for?
A key that is indexed to allow for faster searching
What is normalization?
Normalisation is the process of coming up with the best layout for a relational database
What does normalization try to accomplish?
- Records can be added and removed easily
- Complex queries can be carried out
- No redundancy (unnecessary duplicates)
- consistent data throughout linked tables
What is an index?
An index is a data structure used to look up and access data in a database quickly
What are the requirements to be in First Normal Form (1NF)?
It does not have any repeating attributes.
All the attributes must be atomic (a single attribute cannot more than one data)
e.g. a cell shouldn’t have first name and surname
What are the requirements to be in second normal form (2NF)?
- The database is in 1NF
- There are no partial dependencies (no composite keys)
What are the requirements to be in third normal form (3NF)?
- The database is in 2NF
- There are no non-key dependencies
This can be defined as saying
- ‘All attributes are dependent on the key, the whole key, and nothing but the key’
What does SQL stand for?
Structured Query Language
What is SQL?
A declarative language used to manipulate databases
What is referential integrity?
Referential integrity is the process of ensuring consistency, as it makes sure that information is not removed if it is required elsewhere in a linked database
What is a transaction defined as?
A transaction is a single operation executed on data
What does ACID stand for
- Atomicity
- Consistency
- Isolation
- Durability
What does atomicity (in ACID) mean?
A transaction will be processed completely or not at all
What does consistency (in ACID) mean?
A transaction must maintain referential integrity rules between linked tables
What does Isolation (in ACID) mean?
will ensure that each transaction will be isolated and dealt with in a way that does not affect others
What does durability (in ACID) mean?
Once a transaction has been executed it will remain, regardless of the circumstances
What is record locking?
Record locking is the process of preventing many people to access a record
What is the name of an issue that can happen as a result of record locking?
Deadlock
What is redundancy
The process of creating more than one copy of data in a physically different location
What is a network?
Two or more computers connected together to transmit data
What is physical topology?
The physical layout of the network
What is logical topology?
The topology that describes the flow of data through a network
What is bus topology?
A topology where all terminals are connected to a backbone cable
What is star topology?
A network where the central node directs the flow of data, each terminal is directly connected to the central node
State two advantages of the bus topology
- Cheaper to setup
- Doesn’t require any additional hardware
State two disadvantages of the bus topology
- As traffic increases, performance decreases
- All computers can see data transmissions
- If backbone cable fails, the entire network is disconnected
State two disadvantages of the star topology
- If the central switch fails the rest of the network fails
- Expensive due to switch and cabling
State two advantages of the star topology
- Transmits data faster, so the performance is better
- If one cable fails only that station is affected
- Not difficult to add new stations
- No data collisions
What are protocols?
Protocols are a set of rules defining how two devices communicate with each other
Why are protocols standard?
So that devices from different manufactures are able to communicate
Describe the structure of the internet
The internet is a global network of interconnected networks
What does TCP mean?
Transmission Control protocol
What are the four layers of the TCP/IP protocol stack?
- Application layer
- Transport layer
- Internet layer
- Link Layer
What is the function of the application layer?
The application layer specifies what protocols need to be used
What is the role of the transport layer?
- Splits up data into packets
- Establishes end-to-end connection
What is the role of the network layer?
Add the source and destination IP addresses
What is the function of the link layer?
Adds the MAC addresses to the packets
What is a Local Area Network?
A network spread over a small geographical area
What is a Wide Area Network?
A network spread over a large geographical area
What does DNS stand for?
Domain Name System
What is DNS?
A system used to name and organise internet
resources. Domain names are much easier to remember than IP addresses, which is why they are
used to link to servers across the world
What is the role of a DNS?
The role of the domain name system server (DNS
server) is to translate these domain names into IP addresses when we wish to access a
website.
What is Circut switching?
The process of creating a direct link between two devices and transferring data the entire duration of the link
What is the requirement for circuit switching
The transfer and download rates must be identical on both devices
What is packet switching?
A method of communicating packets of data across a network
Give two advantages of packet switching
- Multiple methods ensure data arrives correctly
- Transfers packetes over a large network
- Mulitple methods to get to a destination, if one method breaks you can go another route
Give an advantage of circuit switching
- Data arrives in order which means data will reconstruct faster
- Allows two people to call without any delay
Give a disadvantage of circuit switching
- Devices must transfer and download at the same rate
- Bandwidth is wasted during periods when no data is sent
What is the purpose of a firewall?
To prevent any unauthorized access to a network
What is a firewall made up of?
- Firewall software
- Two network interface cards
What is the function of a network interface card?
It connects a computer to a network
What is the function of a router?
A router connects two networks together
What is client-server networking?
A relationship between terminals(computers) and a single server, which allow them to communicate, and share resources.
Give an advantage of client-server networking
- Increased security
- Data and resources can be shared
Name a disadvantage of client-server networking
- Expensive to set up
- Trained staff are required to maintain the network
What is peer-to-peer networking?
A network where all terminals are connected to each other to share resources
Give two advantages of peer-to-peer networks
- Cheaper to setup
- Easy to share resources
- Easy to maintain
Give two disadvantages of peer-to-peer networks
- Each computer needs to be backed up independently
- Files and resources are more difficult to share
