What are databases?

What is a database?

• Organized collection of data
• Designed for efficient storage, retrieval and modification
• Data is structured
• Tables, documents, graphs, etc.
• Managed by database software (DBMS)
• Supports multiple users and applications
• Provides data integrity, consistency and security

Where are databases used?

• Web applications
• Mobile applications
• Financial systems and banking
• E-commerce
• Data-analytics and reporting
• IoT and sensor data systems
• Healthcare systems and patient records

Different database types

• Relational databases
  • Table based, fixed schema
• Document databases
  • JSON/XML documents, flexible schema
• Key-value stores
  • Simple key -> value access
• Column-oriented databases
  • Optimized for analytics
• Graph-databases
  • Nodes and relationships
• Time-series databases
  • Optimized for time-stamped data
• In-memory databases
  • Data stored primarily in RAM

SQL databases vs NoSQL databases

SQL databases

• Usually relational
• More traditional
• Data structured as tables
• Transactions
  • Strong data consistency

NoSQL databases

• Relations often optional
• Data can be unstructured
• Do not use SQL (no-sql)
  • Database specific API
• Data consistency is often event level
  • One operation at time

Relational database software

Free software

• MySQL
  • Owed by Oracle
  • Commercial and GPL licenced
• MariaDB
  • Used on this course
  • Open source fork of MySQL
  • Pretty much drop-in replacement for MySQL
• PostgreSQL
  • Open source, more features than MySQL / MariaDB
• SQLite
  • Small / simple
  • Directly supported for example in Python core libraries

Commercial

• Oracle
• Microsoft SQL Server
• MySQL

MariaDB

• Open source fork of MySQL
  • Created when Oracle bought the MySQL
• Same creator as original MySQL has
• Tries to maintain compatibility with MySQL
• Many open source projects have switched to MariaDB
• Has new features that MySQL does not have