**IDEF1X, UML, Crows Feet, etc **
There are a number of standards for creating representations for Entity-Relationship Diagrams that can be used to diagram an ER model, such as IDEF1X (IDEF Overview), UML, Bachman Notation, Martin (a.k.a. “Crows Feet”), and others.
Also the Block Definition Diagram from SysML.