ObjectTypes are a very common modelling concept in OPC UA. Typically, each Companion Specification defines one or more ObjectTypes. Defining an ObjectType makes sense when it is expected that the ObjectType is used several times, either in one Server or across various Servers to provide interoperability on the model.

An ObjectType can be simple without defining any substructure, like the FolderType of the base specification. Typically, an ObjectType defines a substructure with Objects, Variables and / or Methods.