hierarchical_relationship : sub_class_of : Property_Item

This is a root element in the system's internal schema. All relationship (property) classes are children of one of three root relationship types, including this one.

This relationship is used to connect two items, both representing classes, indicating that the subject item is a sub-class of the object item. For example, the connection "Ships is a SubClass-Of Vehicles" links the two class items, and makes the statement that "Ships" are a more specific kind of "Vehicles". Once this connection is established, the system will behave as if everything that is true about "Vehicles" is also true for "Ships" (although not vice-versa). For example, if another property is defined such that its object items are required to be instances of the "Vehicles" class, then having this connection allows instances of "Ships" to be used as well. But, another property whose objects are required to be "Ships" is not affected, and other "Vehicles" still cannot be used.

This category item is the base of the hierarchy of items that are properties. It is a class, and is therefore identified as such by the connection "Property_Item is_instance_of Item_Class". The absolute requirement to identify items as being "property type" (as opposed to individual or category) is to specify that when they are created. However, most properties will also be identified as such by the existence of either the connection "[property] sub_property_of [another property]" or "[property] is_instance_of [another property class]". In the second of these connection forms "another property class" will be either Property_Item or one of its children.