Multiple Document Interface

Graphical computer applications whose windows all reside under a single parent window (usually with the exception of modal? windows), as opposed to each having its own window (Single Document Interface). In the usability community, there has been much debate over which interface type is preferable. Companies have used both interfaces with mixed responses. For example, Microsoft has frequently changed its Office applications from MDI to SDI mode and vice versa.

The disadvantage of MDI usually cited is the lack of information about the currently opened windows: In order to view a list of windows open in MDI applications, you typically have to select a specific menu, if this option is available at all. With an SDI application, the window manager's task-bar or task-manager displays the currently opened windows. In recent years, applications have increasingly added "task-bars" and "tabs" to show the currently opened windows in an MDI application, which has made this criticism somewhat obsolete. When tabs are used to manage windows, individual windows can usually not be resized, which has inspired some people to use a different name for this interface, "Tabbed Document Interface" (TDI).

The acronym MDI is usually not expanded.