Is Opa's graph-based database available separately?

I'm guessing that Opa's graph-based database is written in OCaml. Is it available as a separate project so that it can be used from an OCaml program开发者_运维百科?

Not quite. As the manual explains:

Opa is one technology, consisting of a programming language and its runtime, designed to carry web developers from start to finish of their development, from early prototype to seamless deployment.

So having a separate database was never a goal. However, Opa is written in a modular fashion and the database is a separate component, so I believe using it in a separate project would be mainly a matter of writing an interface layer for it.