This is in addition to the typographical standards described in the last chapter. The following guidelines apply no matter which notation you are using.
When instances of an entity class can be categorized into two or more other entity classes and each of these subordinate classes “inherit” the attributes and relationships of the original entity class, these subordinate classes are called sub-types. The parent class is called a super-type. This concept is known in the object-oriented world as inheritance—each sub-type “inherits” the attributes and relationships of its super-type.