When models reference other models, additional configuration is required using the Build Paths tab.
Build Paths consist of a series of search paths, used to find other models.
Each search path consists of two parts:
Each part of the search path can be omitted. It can consist of a Base variable only, or a search path only.
The model file can be selected using the Browse button next to the Model File text field. Navigate to the desired .opendds model file and hit OK.
Additional search paths can be added through an existing search path's context menu, selecting Add Sibling.