Metamodel Specification Details: Designators This clause specifies the classes of the metamodel in detail. An overview is provided in Clause Overview Metamodel of the Asset Administration Shell. Annex Legend for UML Modelling explains UML modelling together with the specifics used in this specification. Annex D depicts the templates used to describe the classes and relationships. Annex G shows some of the diagrams together with all their inherited attributes to give a complete overview. To understand the specifications, it is crucial to understand the common attributes first (Common Attributes). They are reused throughout the specifications of the other classes ("inherits from") and define important concepts like identifiable, qualifiable, etc. They are abstract, i.e. there is no object instance of such classes. The concept of referencing and how a reference is represented in the UML diagrams and the tables is explained in Clause Environment Attributes and Annex Legend for UML Modelling. Constraints that are no invariants of classes are specified in Clause Constraints: Global Invariants.