Pile of Working Surfaces

Examples:

X-based window managers, and windowing OSes such as Macintosh and Windows
MDI applications (e.g. Word, Excel, Developer Studio)
Physical desktop
Physical bulletin board

Context: The artifact displays anything visual, and can be split up into multiple working surfaces.

Problem: How should the artifact's working surfaces be organized?

Forces:

The user wants easy access to many working surfaces.
There may not be enough space to show them all together.
Each surface may need a different amount of space, or can be resized independently of the other surfaces.
The user can identify them by name or icon, so that they can be brought to the top when needed.
The users generally wants to manage the working surfaces' positions and sizes themselves.

Solution: Stack the surfaces loosely so that they obscure each other most of the time, but so that one or more surfaces of the user's choosing can be on top. If the surfaces look alike when stacked close together, label each surface with a recognizable name or icon (or let the user pick the label). Provide a very simple means by which a user can indicate via the label, and by any part of the surface, "Bring that one to the top." Allow the user to work freely in any of the surfaces, even ones that are not topmost.

Though this pattern is most familiar in the "two-and-a-half-D" context of a desktop GUI, it also works effectively in a more fully 3D environment. 2D working surfaces are still important in this context-- they're needed to view documents, or images, or video clips, for example -- but you now have more freedom to scatter them throughout 3D space, with the added benefits of distance cues and (possibly) more freedom of movement to observe them from different viewpoints. Ben Shneiderman's Designing the User Interface has a picture of one implementation of such a space, Xerox Parc's WebBook/WebForager (pg. 530). However, he also points out that "[a] three-dimensional desktop is thought to be appealing to users, but disorientation, navigation, and hidden data problems remain." [pg. 528]

Resulting Context: To keep things conceptually simple for the user (and for the programmer), use one single "stacking plane" in which the working surfaces appear. This allows any surface to be topmost, and prevents the miserable confusion caused by Windows applications that use two stacking planes -- one on top of the other, each containing multiple working surfaces (MDI child windows in one, dialogs in the other), and no obvious clue to the user that they have to move or get rid of all the dialogs before they can get at the MDI child windows underneath. It's awful for novices, who understandably believe that there is just one stack of windows.

Comments to: jtidwell@alum.mit.edu
Last modified May 17, 1999