The notation was adopted by Barker when he joined Oracle and is effectively defined in his book Entity Relationship Modelling as part of the CASE Method series of books. This notation was and still is used by the Oracle CASE modelling tools.
When Barker started at Oracle, he adopted this notation as part of their practices. The notation is covered extensively in his book "Entity Relationship Modeling," which is included in the CASE Method series. It remains a standard for Oracle's CASE modeling software.