How does column-oriented NoSQL differ from document-oriented?

Question

The three types of NoSQL databases I\'ve read about is key-value, column-oriented, and document-oriented.

Key-value is pretty straight forward - a key with a plain value

Answer 1

The main difference is that document stores (e.g. MongoDB and CouchDB) allow arbitrarily complex documents, i.e. subdocuments within subdocuments, lists with documents, etc. whereas column stores (e.g. Cassandra and HBase) only allow a fixed format, e.g. strict one-level or two-level dictionaries.