An entity alias is a copy of a stock, flow, or converter that allows you to use the original entity elsewhere in your model. The entity alias is not a new, separate entity. Instead, it is a shortcut to the original entity.
Entity aliases (also called ghosts) help you keep your diagrams tidy by allowing you to use the same entity in separate locations in your model. This helps you keep connections neat, as the following pictures illustrate.
Note: You can also use the ghost tool to connect entities across modules and to automatically assign module inputs and outputs.
A ghost of an entity has no independent identity; it is simply an image of the building block from which it was ghosted. The ghosted replica has no equation of its own. When you double-click a ghosted replica, the dialog box that opens belongs to the original entity which the replica was made. No matter how many ghosted replicas of a given building block you create, only one dialog box exists, because only one building block exists.
A ghost adds no real structure to a model. Ghosted stocks have no inflows or outflows; ghosted flows and ghosted converters (when you "ghost" a flow, its ghost appears as a converter) have no input connectors. Ghosts are thus read-only information holders. You can draw connectors from them. Nothing can go into them.
The ghost is available on the Map and Model layers only.
.Click once on the stock, flow, or converter that you want to ghost.
The mouse pointer changes from the ghost pointer 
to a small image of the type of building block you are ghosting.
Click the diagram where you want to place the ghost.
See Also