Brian Ritchie has two posts (☞ here and ☞ here) covering three document databases: CouchDB, MongoDB, and RavenDB concluding with the matrix below: But before using this as a reference material there are a couple of corrections needed: They have some special characteristics that make them kick some serious SQL. Objects can be stored as documents: The relational database impedance mismatch is gone.
![Document Databases Compared: CouchDB, MongoDB, RavenDB](https://cdn-ak-scissors.b.st-hatena.com/image/square/012287c73f3a2ef6e91954367a95b0d5fb615569/height=288;version=1;width=512/https%3A%2F%2F64.media.tumblr.com%2Fa686428e85971c908f38fafbd36a76c5%2Fd9c8f121bc29789a-8b%2Fs500x750%2Fd74ab465b698686cd9f1693eb2cda6b6ca667362.png)