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In an SQL database, the schema and storage of the existing data must be updated as needs evolve. With CouchDB, no schema is required, so new document types with new meaning can be safely added alongside the old. However, for applications requiring robust validation of new documents custom validation functions are possible. The view engine is designed to easily handle new document types and disparate but similar documents.
Distributed
CouchDB is a peer based distributed database system. Any number of CouchDB hosts (servers and offline-clients) can have independent "replica copies" of the same database, where applications have full database interactivity (query, add, edit, delete). When back online or on a schedule, database changes can be replicated bi-directionally.
CouchDB has built-in conflict detection and management and the replication process is incremental and fast, copying only documents changed since the previous replication. Most applications require no special planning to take advantage of distributed updates and replication.
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These replication features can be used in combination to create powerful solutions to many problems in the IT industry. In addition to the fantastic replication features, CouchDB's reliability and scalability is further enhanced by being implemented in the Erlang programming language. Erlang has built-in support for concurrency, distribution, fault tolerance, and has been used for years to build reliable systems in the telecommunications industry. By design, the Erlang language and runtime are able to take advantage of newer hardware with multiple CPU cores.
Next Steps
For installation instructions consult the installation instructions or dive right into the basics if CouchDB is already installed. Detailed information for the more curious can be found in the technical overview.