The existence of an optional entity indicates that its minimum cardinality is zero. The following are the types of the optional entities.
• Super type (optional) is the generalized fundamental entity that shares its attributes and associations with this fundamental entity. This can be the fundamental entity originating from the super type business term that this fundamental entity originates from.
• Sub types (optional) is the fundamental entities that inherit the attributes and associations from this fundamental entity.
• Attributes (optional) is the attributes that describe this fundamental entity. When attributes are united crossways multiple important entities, consider defining a super type fundamental entity to hold the shared attributes and define them only once. These attributes are based on the secondary business terms related to the primary business term that this fundamental entity originates from, and on the description of that primary business term.
• Relationships (optional) is the relationships to other entities. An important unit can be relative of one or more relationships with an associative unit. A fundamental unit can also be right associated to another fundamental entity as a child or a parent when the cardinality is at most a one to many. These relationships are founded on the related main relations to the business term that this fundamental entity creates from.
