An SD model describes a network of dependency relationships among various actors in an organisational context. The actor is usually identified within the context of the model. This model shows who an actor is and who depend on the work of an actor.
An SD model consists of a set of nodes and links connecting the actors. Nodes represent actors and each link represents a dependency between two actors. The depending actor is called Depender and the actor who is depended upon is called the Dependee.