One-to-many and (very rarely) one-to-one relationships can be declared as “identifying” relationships. An identifying relationship is a “stronger” version of the relationship, indicating that the entity at the multiple end of the relationship cannot exist without the entity on the other end.
You can create these relationships using the buttons on the diagram pallet, as well as turn an existing relationship into an identifying one and back again. To do this, either change the Is Identifying property value in the relationship Specification window or select the appropriate check box on its shortcut menu.
An identifying relationship is drawn as a solid line. Non-identifying relationships use heavy dashes.
Dependent / independent entities are a closely related concept. Dependent entities occur at the multiple end of the identifying relationship. They cannot exist without the independent entity at the other end. In addition, every inherited entity (if you are doing ER modeling) is considered to be dependent. A dependent entity's primary key includes the other entity's key as part. This is implied, not shown in the model. Dependent entities are automatically recognized and drawn with rounded corners.