Data type is not model element (Reviewer Review)
Operation return types, parameter data types and attribute data types should be model elements.
Consequences
Using model element data types allows the definition and documentation of data types to be done in one place.
It allows the usage of data types to be checked.
Strategy
If there is not an appropriate data type you may want to create a Basic Type.
Use the Basic Type by using the \u201cSelect…\u201d button on the data type.