A UModel project acts as a container for UML modeling elements, diagrams, and various project-related settings that you may define. UModel projects are saved as files with .ump (UModel Project File) extension.
UModel does not force you to follow any predetermined modeling sequence. You can add any type of model element: UML diagram, package, actor etc., to the project in any sequence (and in any position). All model elements can be inserted, renamed, and deleted in the Model Tree window itself, you are not even forced to create them as part of a diagram.