Rigid-body transformations often provide a good way to place the bases. Work along these lines suggests that the relationship is complicated and non-linear. The sequence is decomposed into 3'-nucleotide monophosphates. Each nucleotide has as independent variables its six helicoidal parameters, its glycosidic torsion angle, three sugar angles, two sugar torsions and two backbone torsions. OCL contains several elements of a molecular modeling language.
Users can create and operate on sets of atoms called objects.
Another nice feature is the equivalence between a literal 3-D point and the position represented by an atom's name. Functions producing values of other data types and stand-alone OCL programs are not possible.