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 began working at Oracle, he incorporated this notation into their practices. The notation is thoroughly discussed in his book "Entity Relationship Modeling" within the CASE Method series. It remains a standard for Oracle's CASE modeling software.