Short for entity-relationship-attribute diagram. A diagrammatic notation for describing and documenting an ERA model. Entities are shown as boxes in the ERA diagram and have an entity name; usually names are required to be unique. Attributes are generally shown as annotations of the entity boxes. Relationships are shown as lines between entity boxes. Markings on the line indicate the name(s) of the relationship, cardinality of the relationship (one to one, one to many, or many to many), and whether the relationship is optional or mandatory. Many software tools for editing diagrams can handle ERA diagrams.