AutomationML models are divided into different hierarchical trees (see Figure 7): InstanceHierarchy, RoleClassLibs, SystemUnitClassLib, and InterfaceClassLib.
The main AutomationML elements and all possible relations between them are shown in Figure 8. The organization in a hierarchical tree involves that every element type can have child elements of the same type (see ChildElement relations). SystemUnitClasses and RoleClasses are defined in an inheritance structure; the RefBaseClassPath relations define such inheritance relations. RoleClasses can be assigned to SystemUnitClasses and InternalElements. In the latter case there are two different ways to make the RoleClass assignment using SupportedRoleClasses or the RoleRequirement. The remaining arrows in Figure 8 describe the possible relations between InternalElements and SystemUnitClasses. An InternalElement can inherit from a SystemUnitClass. In the scope of AutomationML SystemUnitClasses are only templates and can be changed after instantiation. The backward relation indicates that a SystemUnitClass can define sub-elements in terms of InternalElements. These sub-elements (InternalElements) should be included on instantiation. RoleClasses describe functions of a physical or logical plant object independent of a technical implementation. They offer a possibility to specify an object in an abstract way and independent of the manufacturer. The assignment of a RoleClass to an object (SystemUnitClass or InternalElement) results in the allocation of fundamental functions or requirements.
Figure 9 depicts the basic structure of a RoleClass (RC), SystemUnitClass (SUC), or InternalElement (IE). Each can contain arbitrary nested Attributes and Interfaces (see ChildElement relations). The Interfaces are called ExternalInterfaces and shall inherit from an InterfaceClass. They can be connected to other ExternalElements via InternalLinks. The InterfaceClasses are stored hierarchically and shall have independent inheritance relations. InterfaceClasses and certainly ExternalInterfaces may also have arbitrary nested Attributes.