A Scale_element is a relationship between a Independent_property_definition and a Maths_value; and that is a member of a Scale.
A Scale_element identifies a Independent_property_definition by a Maths_value.
EXPRESS specification:
*) ENTITY Scale_element; identifier : Maths_value; property : Independent_property_definition; END_ENTITY; (*
Attribute definitions:
identifier : the Maths_value that corresponds to the property.
property : the Independent_property_definition that corresponds to the identifier.