BSONdocument

BSONdocument, commonly referred to as a BSON document, is a binary-encoded serialization of JSON-like documents used primarily in MongoDB and related ecosystems. It stores data in a compact, machine-friendly format, enabling efficient storage, transmission, and in-memory processing.

A BSON document consists of a 32-bit little-endian total size field, followed by a sequence of elements. Each element begins with a single byte indicating its type, followed by a cstring key (UTF-8, terminated by a NUL byte), and then the value encoded according to its type. The document ends with a NUL terminator. Documents may be nested to form complex structures.

BSON supports a rich set of data types beyond JSON, including double, string, embedded document and array, binary data, ObjectId, boolean, date, null, regular expression, int32, int64, and decimal128, as well as special types like minKey and maxKey. Some legacy types such as undefined, DBPointer, and symbol exist in older specifications. Arrays are encoded as documents with numeric keys.

In practice, BSONdocument is the wire format and storage format used by MongoDB drivers and servers, permitting fast encoding/decoding and efficient traversal. In MongoDB, there is a practical maximum document size of 16 megabytes, though larger composite data structures can be built from multiple documents. BSON is also used by other systems and libraries that require a binary, schema-flexible representation of data.

Compared with JSON, BSONdocument is binary and type-rich, which reduces parsing overhead and preserves type information but at the cost of human readability. It is designed for fast machine processing and compactness, while maintaining compatibility with JSON-like structures. See also BSON, MongoDB, JSON, and binary serialization formats.