Freebase - API Reference

Freebase contains at this time of writing more than 10 million topics, more than 3000 types, and more than 30,000 properties. This is not a small database by any measure. If you were to think of it in terms of relational databases, it is probably the database with the most number of relational tables (3000+ types), and the most number of table columns (30,000+ properties).