1.3 Exchanging Data Flashcards
(50 cards)
What is the purpose of compression?
The purpose of compression is to increase the amount of files within the same amount of storage
What is lossy and lossless compression
Lossy compression is reducing the size of a file whilst completely removing some of its information
Lossless compression is reducing the size of a file less then lossy but doesn’t lose any of its information if returned to its normal size
What are the types of lossless compression?
Run Length Encoding
Dictionary Encoding
What is Run Length Encoding?
Repeated values are replaced to make one part of data followed by the amount of times it repeated.
For example AAAAAAAA is A8
What is dictionary encoding?
Frequently appearing pieces of data are replace with a number and the data is then stored in a dictionary which matches the number that represents it.
What is encryption?
Encryption is used to make data secure especially when transmitting data to a destination.
What are the two types of encryption?
Symmetric
Asymmetric
What is Symmetric encryption?
Both the sender and user share the same private key. With this they can encrypt and decrypt data. To access data they can exchange a private key in a key exchange meaning the user can then decrypt the data. This does cause potential issues such as if the private key were to be intercepted.
What are the two types of encryption?
Symmetric
Asymmetric
What are the two types of encryption?
Symmetric
Asymmetric
What is asymmetric encryption?
In this process two keys are used. A private key and public key. The public key can be used anywhere whilst the private key must be kept secret. They two keys are a pair and are mathematically related
What is the relational database?
A database which recognises the difference between entities and therefore has different tables for each entity
What is hashing?
Hashing is a process where data is turned into a fixed size called a hash. In terms of encryption this is a one way encryption. Meaning it can not be hacked so easily ans can’t be reversed to form a key. Another way hashing is used is a hash table. A hash table takes the hashed numbers and forms it into an array. With this array data can be looked up using the hash function. An issue with hash tables is the chance of collisions where two different data’s are both hashed to the same figure. Ways to overcome are storing interns in a list or using a second hash function to generate a new hash
What are entities?
Entities are an item of interest where info is stored.
What is a flat file database?
A flat file database is a database which consists of a single file. Around a single entity and its attributes.
What is a primary key?
A primary key is a unique identifier for a record in a table
What is a foreign key?
A foreign key is an attribute linking two tables together. In one table as a primary key in another as a foreign key in the other.
What is a secondary key?
Secondary key allows for databases to be searched quickly.
What are the different types of entity relationship models?
One to one
Many to one
Many to many
What is normalisation?
Normalisation is the process of coming up with the best layout for a relational database.
What does normalisation aim to accomplish?
1NF is there must be no attributes with more that one value
2NF is that 1NF must be accomplished and there are no partial dependencies. No attributes can depend on a part of a composite key
3NF is the 2NF must be accomplished and there is no non key dependencies. Attributes only depend on a composite key.
What are the stages of normalisation?
1NF is there must be no attributes with more that one value
2NF is that 1NF must be accomplished and there are no partial dependencies. No attributes can depend on a part of a composite key
3NF is the 2NF must be accomplished and there is no non k
