In graphical user interfaces, a single document interface or SDI is a method of organizing graphical user interface applications into individual windows that the operating system's window manager handles separately. Each window contains its own menu or tool bar. This contrasts with a multiple document interface, in which a single parent window is used to contain multiple nested child windows, with only the parent window having a menu or tool bar.
Often in single document interfaces, each window is represented as an individual entry in the operating system's task bar or manager. Applications which allow the editing of more than one document at a time, e.g. word processors, may therefore give the user the impression that more than one instance of an application is open. Some task managers summarize windows of the same application. For example, Mac OS X uses a feature called Exposé which allows the user to temporarily see all windows belonging to a particular application.