When should I use an object database?

Question

I have been using relational databases for some time now and recently came across a different type of database: object database. One of the products built around this idea had a description: A scalable, "post-relational" database with a multidimensional data and application server for distributed web applications.

This makes me wonder, when am I supposed to use such a database? I mean, Facebook must be using MySQL and it seems to be doing fine and it can be considered a large-scale distributed web application. The same goes for some other web applications such as Twitter and Orkut perhaps. Given that this is the case, when am I supposed to use an Object database?

Answer 1

Object databases work really well when you have deep object graphs (e.g., CAD or finite element models with lots of geometric entities). Doing all those JOINs in a relational database would be prohibitively expensive, but it's natural for an object database.