It is allowed to create new subtypes of existing DataTypes.

It is not recommended to insert types inside the type hierarchy of DataTypes (similar to ObjectTypes and VariableTypes, see Figure 1). If absolutely necessary, the following rules apply:

• For all DataTypes no new constraints (written as text in the specification) should be added, but existing constraints common to all the subtypes can be added to the new supertype.
• For abstract DataTypes there are no additional rules.
• For simple DataTypes (using the encodings of the built-in DataTypes) there are no additional rules.
• For Enumeration DataTypes the new supertype may have more Enumeration Values than the subtypes. In that case, it shall have at least a union of all Enumeration values defined in any of its subtypes. If the numeric values would conflict, it is not possible to create such a supertype.
• For Structured DataTypes, the supertype shall only have fields that are already defined in all subtypes. It shall be legal to create all existing subtypes, considering DataType, ValueRank and ArrayDimensions.