This feature enables you to manually add or delete entities or relationships from models.
It also allows you to manually add, edit, or remove properties
and modify values for properties associated with entities and
relationships. An example of this functionality might be that if
your model uses data for the United States of America and one of
the entity properties for a state is population, you could
change its value if for some reason the population has changed
since your model was created. After you edit your model you can simply click Save to apply
the changes to the existing model, or you can click Save As to
save the edited model under a new name.