Graph Databases, Column Stores, Key Value Stores and Document Databases

Question 1

Graph databases

Answer 1

This shows data as a mathematical graph

Question 2

Advantages and Disadvantages of Graph Databases

Answer 2

• Used in data science as well and can really focus on relationships
• Often used as parts of larger systems to show the relationships
• However, can be issues with scaling as the graph gets bigger

Question 3

Column Stores

Answer 3

They have tables like relational databases but data is stored in columns, not rows. not all rows will have the same number of columns

Question 4

Advantages of Column Stores

Answer 4

• The performance of searching for a specific column is much faster
• It is able to retrieve all info from a column very quickly

Question 5

The Disadvantages of Column Stores

Answer 5

• The performance of searching for a specific row is much slower
• The performance of adding a new row is not as good as a new value would have to be added to each of the columns

Question 6

Hashing

Answer 6

• to directly search the location of desired data on the disk without using index structure

Question 7

Advantages and disadvantages of hashing

Answer 7

• Can think of a hash table as being like an array

* BUT – a poor hash function can lead to key collisions

Question 8

Key value stores

Answer 8

• Also known as a Dictionary, rather than a hash table
• The idea is that a simple key maps to a more complex value
• Is like an array of keys
• The values are the records in the table
• The records can have different fields to each other unlike a relational DB

Question 9

Keys in key value stores

Answer 9

• Keys need to be unique to prevent the problem of key collisions
• Keys should not be too long for performance reasons

Question 10

Values in key value stores

Answer 10

• The values can be anything – different databases permit different
data types

• However, can also be more complex such as sets, lists, code, images
or even key-value pairs again encapsulated in an object

Question 11

Advantages of key value stores

Answer 11

Performance - querying is very quick

Data Variation- values can be different from each other

Question 12

Disadvantages of key value stores

Answer 12

Lack of referential integrity - data in different values can contradict each other

Basic querying only - three operations: PUT, GET, DELETE

Question 13

Document Databases

Answer 13

• Use document oriented model to store data
• They are self contained
• Similar to key value stores as they have keys

Question 14

Advantages of Document databases

Answer 14

• Good if the data is varied – the documents can all contain different fields
• Key-value storage approach offers quick performance – fast to load and store documents

Question 15

Disadvantages of document databases

Answer 15

Basic operations only- more advanced as key value store but not as advanced as SQL
No normalisation