In Rational® XDE,
you can create association classes to model additional information about association
relationships. While you can model the same construct in the Rational modeling
products, the implementation is different between the tools.
Association class model elements before import
In
the screen captures later in this topic, the first figure represent XDE, while
the second figure represents the same diagram or construct in the Rational modeling
products after import.
In XDE, an association class is built from five
model elements, as shown in the following figure: two end classes (A and B),
an association between them (the solid line), the association class itself
(AC), and the AssociatedClass relationship (dashed line) from the association
to the association class (AC).

Association class model elements after import
After
import, the association class construct has changed so that the association,
the associated class (AC), and the relationship (dashed line) are represented
by one single element: an AssociationClass element named AC. In UML 2.0, an
AssociationClass element is both an association and a class, and it is displayed
as both on diagrams. Several other important changes also take place during
the import process:
- Because multiple XDE elements are merged into a single UML 2.0 element,
you have less control over the display of association classes on diagrams.
For example, the characteristics of the dotted line connecting the association
with the class, such as color and bend points, are not imported because there
is no element in UML 2.0 to which those characteristics can be applied.
- Sometimes the XDE class that is part of the association class is transformed
into the UML 2.0 association class and no longer exists as a separate class.
In other cases, such as if the class and the association live in different
packages, the class is migrated separately and its contents are merely copied
into the association class. The diagram in the following figure capture shows
an example of the latter, where the class is copied rather than transformed.

Note: Diagrams that contain
association classes are more likely than other diagrams to require manual
repositioning of elements and labels after migration. In this figure, the
AC class created after import was manually moved from underneath the association
class.