Use the Domain classes dependencies diagram for creating and editing relationships between the domain classes.
The diagram is completely synchronized with the source code: the changes in the source code are immediately reflected in the diagram, and vice versa, adding or deleting a link in diagram introduces relevant changes to the source code.
- Select the desired domain class, and click the Domain classes dependencies tab that is located on the bottom of the editor.
- Click the source domain class and draw a link to the target domain class:

- In the dialog box that opens, specify the type of relationship, and the name of the field to be created:

The resulting relationship is displayed in diagram:
