BSON

BSON [bee · sahn], short for Bin­ary JSON, is a bin­ary-en­coded seri­al­iz­a­tion of JSON-like doc­u­ments. Like JSON, BSON sup­ports the em­bed­ding of doc­u­ments and ar­rays with­in oth­er doc­u­ments and ar­rays. BSON also con­tains ex­ten­sions that al­low rep­res­ent­a­tion of data types that are not part of the JSON spec. For ex­ample, BSON has a Date type and a BinData type.

BSON can be com­pared to bin­ary inter­change for­mats, like Proto­col Buf­fers. BSON is more "schema-less" than Proto­col Buf­fers, which can give it an ad­vant­age in flex­ib­il­ity but also a slight dis­ad­vant­age in space ef­fi­ciency (BSON has over­head for field names with­in the seri­al­ized data).

BSON was de­signed to have the fol­low­ing three char­ac­ter­ist­ics:

1. Lightweight

   Keep­ing spa­tial over­head to a min­im­um is im­port­ant for any data rep­res­ent­a­tion format, es­pe­cially when used over the net­work.

2. Traversable

   BSON is de­signed to be tra­versed eas­ily. This is a vi­tal prop­erty in its role as the primary data rep­res­ent­a­tion for Mon­goDB.

3. Efficient

   En­cod­ing data to BSON and de­cod­ing from BSON can be per­formed very quickly in most lan­guages due to the use of C data types.

What is the point of BSON when it is no smaller than JSON in many cases?

BSON is designed to be efficient in space, but in many cases is not much more efficient than JSON. In some cases BSON uses even more space than JSON. The reason for this is another of the BSON design goals: traversability. BSON adds some "extra" information to documents, like length prefixes, that make it easy and fast to traverse.

BSON is also designed to be fast to encode and decode. For example, integers are stored as 32 (or 64) bit integers, so they don't need to be parsed to and from text. This uses more space than JSON for small integers, but is much faster to parse.

http://bsonspec.org/