database

A database is an organized collection of data stored and accessed electronically. Databases are designed to store large amounts of information and to support efficient storage, retrieval, modification, and deletion of data. Access is typically provided by a database management system (DBMS), which offers a query language, data definition and manipulation tools, and security controls. Data is modeled according to a data model; the relational model, which uses tables, rows, and columns, is the most widely used. In relational databases, relationships are expressed through keys and constraints, and SQL is the standard language for querying and updating data. Other models include document stores, key-value stores, column-family stores, and graph databases, each optimized for different workloads and access patterns.

Core concepts include ACID properties—Atomicity, Consistency, Isolation, and Durability—that ensure reliable transaction processing. Transactions group multiple operations into a single unit that either fully succeeds or has no effect. Database design often employs normalization to reduce data redundancy and improve integrity; denormalization may be used to optimize read performance in certain scenarios. Schema definitions, constraints, indexing, and access controls help manage data quality and security.

Architectures range from centralized to distributed, with replication, partitioning (sharding), and parallel query processing to improve scalability and availability. The CAP theorem describes trade-offs among Consistency, Availability, and Partition tolerance in distributed systems. Modern databases include traditional relational systems, NoSQL families, and cloud-native managed services.

Common use cases span transaction processing, analytics, content management, and scientific data storage. Good database design emphasizes data independence, allowing applications to evolve without being tied to physical storage details.