transaction
A transaction is a group of queries that must be either completed or rejected as a whole. Execution of some, but not all, queries results in inconsistent or incorrect data.
architecture
The architecture of a database system describes the internal components and the relationships between components.
query processor
The query processor interprets queries, creates a plan to modify the database or retrieve data, and returns query results to the application.
query optimization
The query processor performs query optimization to ensure the most efficient instructions are executed on the data.
storage manager
The storage manager translates the query processor instructions into low-level file-system commands that modify or retrieve data.
indexes
The storage manager uses indexes to quickly locate data.
transaction manager
The transaction manager ensures transactions are properly executed.
log
The log is a file containing a complete record of all inserts, updates, and deletes processed by the database.
catalog / data dictionary
The catalog, also known as a data dictionary, is a directory of tables, columns, indexes, and other database objects.
relational database
A relational database stores data in tables, columns, and rows, similar to a spreadsheet.
SQL
SQL stands for Structured Query Language and includes statements that read and write data, create and delete tables, and administer the database system.
big data
The growth of the internet in the 1990s generated massive volumes of online data, called big data, often with poorly structured or missing information.
NoSQL
The newer non-relational systems are called NoSQL, for 'not only SQL', and are optimized for big data.
Open source
Open source software is software that anyone can inspect, copy, and modify with no licensing fee.