Can you explain what is meant by transactions in database management systems?

A transaction in database management systems is a sequence of operations that are executed as a single unit. It has four main properties (ACID):

• Atomicity: all operations of the transaction are completed fully or not at all.
• Consistency: after the transaction completes, the database remains in a correct state.
• Isolation: concurrent transactions do not affect each other.
• Durability: after a transaction is committed, its changes are permanent even in case of failures.

Example in Python using SQLite:

import sqlite3

conn = sqlite3.connect('example.db')
cursor = conn.cursor()

try:
    conn.execute('BEGIN')
    cursor.execute("INSERT INTO users (name) VALUES ('Alice')")
    cursor.execute("INSERT INTO accounts (user, balance) VALUES ('Alice', 1000)")
    conn.commit()  # Commit the transaction
except Exception as e:
    conn.rollback()  # Rollback in case of error
    print('Error:', e)
finally:
    conn.close()

Here, both insert operations either execute together or not at all.