To clarify this comment a bit: The conventional RDBMSs people refer to as relational databases (Oracle, Postgres, MySQL, SQLite, etc.) shoot for compatibility with the SQL standard, which diverges from the relational model. For example, you can have duplicate rows in a table, which doesn't make any sense in the (set-based) relational model. SQL is not "purely" relational.
If you read Chris Date's books (I recommend starting with _An Introduction to Database Systems_), he really hammers this point.
There are people who hate SQL because it's too relational, and there are people who hate SQL because it's not relational enough.