Flashcards in 1.3 Exchanging Data Deck (39):
Define and explain lossy compression
Lossy compression is a way of reducing the file size by deleting irrelevant data. The data is lost and the original cannot be recreated. This reduces the quality
Define and explain lossless compression
Data from the file is not lost and the original can be easily recreated. Records patterns in the data and stores instructions on how to recreate the file
What is run length encoding?
Used with images. The data can be stored as a list of colours, counting the number of repeating patterns
What is dictionary coding?
Used mainly for text and software applications where no data is irrelevant. The data is stored in a dictionary style. The word is stored once and referenced to reduce the amount of data stored.
What is the difference between symmetric and asymmetric encryption?
symmetric - if the key is intercepted the message is easily de-cryptable as the same key is used to encrypt and decrypt the data
Asymmetric - a user has a private and public key which is unique, the user only ever sends the public key to encrypt a message and decrypts the message using the private key which is never sent
What is encryption?
The process of encoding the message so that it can only be read by the sender and the intended recipient.
What is an encryption key?
The data is encrypted using an encryption key. If the data is intercepted, it cannot be deciphered unless they have the key.
What is hashing?
Data is converted into a number or string similar to encryption however the data is unable to be converted back to its original input. If the output is the same you can assume that the passwords match.
What is the difference between encryption and hashing?
Encryption makes a message unreadable to users that should not be allowed access unless they have the key whereas hashing coverts an input into an output and cannot be reversed. Can be used for checking and storing passwords as well as determining where to store data i.e. hash tables
What is a hash function?
Used to generate the output. The output will be the same every time a string is entered providing you enter the same string each time.
Define what a relational database is
a database that links tables through primary and foreign keys including attributes and entities
Define what a flat file database is
made as lists like a spreadsheet. Flat file databases are often prone to data redundancy however they are fine for small amounts of data
Define primary key
unique identifier of an entity
Define what an entity relationship diagram is
A data modelling diagram technique used to define a relational database
What is database normalisation?
Organising attributes and relations of a relational database to minimise data redundancy
What is database indexing?
Used to speed up searching. sequentially searches through the data. Like an index in a book
What are the rules of 1NF?
Remove duplicate data
Needs a primary key
What are the rules of 2NF?
Must be in 1NF
A composite key is usually created
Remove data sets that occur in multiple rows
What are the rules of 3NF?
Must be in 2NF
All data has to rely on the primary key
What is SQL?
Structured Query Language - used to communicate and create databases
Name 3 SQL commands and explain what they do
What is meant by referential integrity?
Adds constraints to the data updated, deleted and entered into a relational database to ensure that the data is as accurate as possible uses cascade updates and prevents deletion of a record that is a foreign key of another table
What is ACID?
A set of properties to ensure that the integrity of the database is maintained under all circumstances. It guarantees that transactions are processed reliably
What is atomicity?
Requires a transaction to be processed in its entirety or not at all. It makes it impossible to process only part of a transaction
What is consistency?
Ensures that no transaction can violate any of the validation rules. Therefore referential integrity will always be upheld
What is isolation?
Ensures that the execution of transactions leads to the same results as if they were processed one after another. Crucial in a multi-user database
What is durability?
Ensures that once a transaction has been committed, it remains even in the even of a power cut. As each part of the transaction is completed, it is held in a buffer on a disk until all elements are completed. Only then will changes be made to the database.
What is a multi-user database?
allows multiple users to simultaneously access a database. This could potentially cause updates to be lost if more than one user is editing the database at a time
What is record locking?
Prevents simultaneous access to the database to prevent updates being lost or inconsistencies in the data arising. However if two users are attempting to update two records deadlock can occur
What is serialisation?
Prevents deadlock. This ensures that the transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost.
What is timestamp ordering?
Every object in the database has a read and write timestamp. These are updated whenever an object is written or read. When a user tries to save an update the DBMS knows that another user has accessed the object is the timestamp is not the same as when they started
What is database redundancy?
What a part of the system fails, the machine becomes redundant. We can create duplicate hardware that mirrors every transaction that takes place and can automatically take over if the main system fails
Why is it important that networks have protocols and standards?
Protocols are rules and standards that govern data transmission. They ensure that devices can talk to each other. 4 layers
Application - concerned with production and reception of data. Packages data and passes to transport layer
Transport - makes and breaks connections via routers
Internet - Provides links across different network types
Link - Passes data to the physical network.
Describe the TCP/IP stack
Transmission Control Protocol/ Internet Protocol - Used to bring order to the internet as well as many private networks.
What is meant by a client-server network?
High end computers acting as servers which provide service to the users/clients. This includes; file storage and access, printing, internet access and security features. Adds more control over the network
What is meant by a peer to peer network?
Each computer has an equal status. It is generally cheap and not a very common way of implementing a network. Easy to pass files between the users without having to go through a server. Can make use of distributed computing for collaborative working
What is HTML?
HyperText Markup Language - a text-based language that uses tags, producing basic web pages using any plain text editor
What is CSS?
Cascading Style Sheets - Defines how HTML elements are to be displayed. CSS files are stored separately from the HTML they affect