Topic 3

• What is the purpose of compression in file storage?


  To reduce the storage space required by a file
• Why is compression particularly important for sharing files over networks?


  It increases the number of files that can be transferred in a given time
• What is an example of an app that uses compression for file storage?


  Google Photos
• How does downloading a compressed file compare to downloading the full version?


  Downloading a compressed file is faster
• What are the two categories of compression?

  • Lossy compression
  • Lossless compression
• What happens to a file during lossy compression?


  Some information is removed, potentially degrading quality
• What is a potential consequence of lossy compression on images?


  It can result in a more pixelated image
• How does lossless compression differ from lossy compression?


  Lossless compression reduces file size without losing any information
• What can be done with a file after it has been compressed using lossless compression?


  The original file can be recovered from the compressed version
• How does lossy compression work with audio files?


  It removes very high or low frequencies that are least noticeable
• Why can't you recover the original file from a lossy compressed version?


  Because some information is completely disregarded
• What does RLE stand for in compression methods?


  Run Length Encoding
• How does run length encoding (RLE) work?


  It replaces repeated values with one occurrence followed by the count
• How would the string AAAAAABBBBBCCC be represented using RLE?


  A6B5C3
• What is a limitation of run length encoding?


  It doesn't offer great reduction if there's little repetition
• What is dictionary encoding in compression?


  • Replaces frequently occurring data with an index
  • Compressed data is stored alongside a dictionary
  • Original data can be restored using the dictionary
• How does dictionary encoding reduce the size of a passage?


  By replacing phrases with their corresponding index
• What must be transferred alongside data compressed using dictionary encoding?


  The dictionary
• What is the purpose of encryption?


  To keep data secure during transmission
• What are the two types of encryption discussed?

  • Symmetric encryption
  • Asymmetric encryption
• In symmetric encryption, what do the sender and receiver share?


  A private key
• What is a key exchange in symmetric encryption?


  A process where the private key is distributed between sender and receiver
• What is a risk associated with symmetric encryption?


  If the private key is intercepted, communications can be decrypted
• How does asymmetric encryption differ from symmetric encryption?


  It uses a public key and a private key
• What is a key pair in asymmetric encryption?


  A public key and a private key that are mathematically related
• What must someone do to send you a message using asymmetric encryption?


  Find your public key
• What happens when a message is encrypted with a recipient's public key?


  Only the recipient's private key can decrypt it
• How can you prove that a message was sent by you in asymmetric encryption?


  By encrypting it with your private key
• What is hashing?


  • A process that turns an input (key) into a fixed size value (hash)
  • Uses algorithms called hash functions
  • Output cannot be reversed to form the key
• Why is hashing useful for storing passwords?


  Because the output cannot be reversed to gain the original password
• What is a hash table?


  • A data structure that holds key-value pairs
  • Formed from a bucket array and a hash function
  • Used for constant time data lookup
• How do hash tables achieve constant access times?


  By using a hash function to store data in buckets
• What is a collision in hashing?


  When two keys produce the same hash
• What are some methods to overcome collisions in hashing?


  Storing items together in a list or using a second hash function
• What characteristics should a good hash function have?


  Low chance of collision and quick to calculate
• Why should the output of a hash function be smaller than the input?


  To ensure searching for the hash is faster than searching for the key
• What is an entity in a relational database?


  An entity is an item of interest about which information is stored.
• How does a relational database recognize differences between entities?


  By creating different tables for each entity.
• What does an entity relationship model illustrate?


  • It shows entities and their relationships.
  • Example entities: Doctor and Patient.
  • Attributes link tables together, e.g., DoctorID.
• What are attributes in a relational database?


  Attributes are characteristics of the entity; categories about which data is collected.