Fortran 90 supports supertypes meaning that user-defined types can include other defined types and a hierarchy can be built up in this way, however, this does not apply in the other direction, Fortran 90 does not have subtypes. Due to the lack of subtyping functional and object inheritance cannot be transmitted in this fashion, however, ADA has subtypes but is still not considered to be an object oriented language. Being able to define subtypes which inherit access functions from the parent type is a very important aspect of object oriented programming and Fortran 90 does not support this.