## 7.1 General

Typically, the components of a complex VariableType are fixed and can be extended by subtyping. However, because each Variable of a VariableType can be extended with additional components this standard allows the extension of the standard VariableTypes defined in this document with additional components. This allows the expression of additional information in the type definition that would be contained in each Variable anyway. However, it is not allowed to restrict the components of the standard VariableTypes defined in this International Standard. An example of extending VariableTypes would be putting the standard Property NodeVersion, defined in OPC 10000-3, into the BaseDataVariableType, stating that each DataVariable of the Server will provide a NodeVersion.