Database Fundamentals

Question 1

What are RDBMS?

Answer 1

o Relational Database Management Systems (RDBMS) are used when the data to be managed has formal and fixed relationships. Data is stored on disk as rows, and entire rows must be parsed even if individual attributes are all that is needed
o Every table has a schema that defines a fixed layout for each row, which is defined when the table is created. Every row in the table needs to have all the attributes and the correct data types
o RDBMS conforms to the ACID System: Atomicity, Consistency, Isolation and Durability. This impacts the ability to achieve high performance levels and limits scalability
o SQL (Structured Query Language) is used to interact with most SQL (relational) database products
o RDBMS systems were developed when memory was the most expensive resource, so the objective was to avoid data redundancy with data normalisation. With CPU becoming the most expensive resource, there is a move towards no-SQL databases

Question 2

What are the main No-SQL Databases?

Answer 2

 Key Value (e.g. AWS DynamoDB): Data is stored as key and value pairs. It offers super fast queries and ability to scale. No relationships and weak schema
 Document (e.g. MongoDB): Data is stored as structured key and value pairs, called Documents. Operations on documents are highly performant
 Columnar (e.g. AWS RedShift): Data is stored in columns, rather than rows. Queries against attribute sets, such as all DOBs or all surnames, are fast. Great for data warehousing and analytics
 Graph (e.g. Neo4j): Designed for dynamic relationships, stores data as nodes and relationships between those nodes. Ideal for human-related data, such as social media