Unit 4: Exchanging Data Flashcards
Describe Compression and it’s uses.
Compression is the process used to reduce the storage space required by a file.
It is important for sharing files over networks or the Internet because it increases the number of files that can be transferred (downloaded / uploaded) in a given time.
Describe the difference between Lossy vs Lossless Compression
Lossy compression reduces the size of a file while also removing some information (e.g MP3, OGG)
Lossless compression reduces the size of a file without losing any information (e.g WAV, FLAC)
What is Run Length Encoding?
Run Length Encoding is a method of lossless compression which repeated values are removed and replaced with one occurence followed by the number of times it should be repeated.
What are the drawbacks of Run Length Encoding?
● Relies on consecutive pieces of data being the same
● Doesn’t offer a great reduction in file size if there’s little repetition
What is Dictionary Encoding?
Dictionary Encoding is a method of lossless compression where frequently occurring pieces of data replaced with an index.
Compressed data is stored alongside a dictionary. Because the dictionary matches frequently occurring data to an index, original data can be restored using the dictionary.
What is the main use of encryption?
To keep data secure when it’s being transmitted
Describe Symmetric Encryption.
● Both sender and receiver share the same private key
● The key is distributed in a process called a key exchange
As the key is used for both encrypting and decrypting data, the key must be kept secret; if the key is intercepted then any communications sent can be intercepted.
Describe Asymmetric Encryption.
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.
Messages encrypted with the recipient’s public key can only be decrypted with the recipient’s private key, which should only be in the possession of the recipient.
What is Hashing?
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). There are a vast number of algorithms, called hash functions, which do this.
Describe how Hashing can be used to store passwords.
Unlike encryption, the output of a hash function can’t be reversed to form the key. A password entered by a user can be hashed and checked against the key to see if it is correct, but a hacker would only gain access to the keys, which can’t be reversed to gain the passwords.
What is a relational database?
A relational database is a database which recognises the differences between entities by creating different tables for each entity.
What is a flat file database?
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…)
What is a primary key?
A primary key is a unique identifier for each record in the table. The primary key is shown by underlining it.
What is a foreign key?
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. In example (1), DoctorID is the foreign key in the Patient table. The foreign key is shown using an asterisk.
What is a secondary key?
A secondary key allows a database to be searched quickly. Looking at example (1), 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.
What are the three types of table relationships?
- One-to-one
- One-to-many
- Many-to-many
