1.3 Exchanging Data Flashcards
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
SELECT
DELETE
UPDATE
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?
Atomicity Consistency Isolation Durability 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
