Metaphors in Computing: Desktop and Touch

When we encounter new technology, its purpose and operation may seem obvious, but learning often relies on prior experience and familiar cues. This is the idea behind the section title “What We See and What We Think.”
Metaphors help us learn quickly by mapping new interfaces to familiar shapes and controls (e.g., a volume control for other increasing/decreasing quantities).
A metaphor is an icon, image, or concept that represents a computation or operation; designers use metaphors to reduce the need to read a manual.

Designers minimize learning time by using familiar metaphors (e.g., a slider that looks like a volume control).
Our expectations are reinforced by conventions (e.g., low values on the left or counterclockwise; high values on the right or clockwise).
Metaphors are especially common in software; they help users operate without reading manuals.

The Alto at Xerox PARC introduced a graphical user interface (GUI) to replace the command-line interface (CLI).
CLI uses a militaristic metaphor of a sequence of typed commands; GUI presents a desktop-like workspace with windows.
GUI concepts: virtual desktop, overlapping windows, scroll bars, icons, and window clipping.

The mouse was invented by Douglas Engelbart in $1967$ and publicly demonstrated in $1968$ in what’s called “The Mother of All Demos.”
Alto’s GUI popularized the mouse and desktop metaphor for office use.
Apple’s Macintosh, introduced in $1984$ , extended the Alto ideas with more icons and windowed interaction; it helped popularize the desktop metaphor on a personal computer.

As computers became mobile, the mouse became less practical and a touch metaphor emerged.
The stylus offered one solution, but touch became the dominant approach for handheld devices.
Cover Flow is a touch metaphor example: a finger sweep across a sequence of items causes them to stream by, with a center item identified as selected.

Sweep or Swipe — Description: Move finger across surface; Typical Use: Scan through a list; Typical Result: Items sweep by, with one selected
Tap — Description: Light one-finger tap on surface; Typical Use: Select; Typical Result: Item identified
Double Tap — Description: Light two-finger tap on surface; Typical Use: Launch; Typical Result: Launch
Drag — Description: Move selected item by pulling; Typical Use: Move item; Typical Result: Item in new position
Pinch — Description: Fingers/Pull Fingers Apart; Typical Use: Contract/expand; Typical Result: Shrink/zoom
Two-Finger Scroll — Description: Move fingers across surface; Typical Use: Navigation; Typical Result: Move around a clipped image
Flick — Description: Quick sweep, finger leaves surface; Typical Use: Express acceleration; Typical Result: Acceleration
Sustained sweep — Description: Fluency Bit; Typical Use: (as listed); Typical Result: (as listed)

Metaphors leverage our physical-world experience; the entire UI can be created, not constrained by physical hardware, so controls can take any form.
Skeuomorphism is the design approach of making digital things resemble real-world objects; it has both advantages and drawbacks.
Touch represents a fundamental shift in interaction, not just a minor extension of the desktop; it changes how we think about interacting with computers.

Touch is not merely an add-on to the desktop; it requires rethinking how users interact with content.
Navigation with touch differs from the desktop metaphor in how content is manipulated and viewed.
Multitouch trackpads extend touch gestures into desktop/laptop contexts, enabling touch-like motions on larger devices.

Desktop metaphor uses scroll bars to navigate long content; touch metaphor uses direct manipulation of content via swipes.
Direction of motion differs between metaphors: in touch, you sweep finger left to go later in a list; in desktop, you roll a scrollbar or move a window to reveal later items.
These differences reflect the underlying metaphors: you touch the content vs you slide a window over the content.
The two metaphors coexist and shape how users think about and interact with devices.

Metaphors are 100 percent synthetic constructs designed to simplify use across devices (desktops, tablets, phones).
The desktop metaphor is classic; the touch metaphor is newer and continues to grow in importance.
Both metaphors will continue to coexist in daily computing.
See Table 2.1 and your own experience to understand how these metaphors influence operations like zooming in.

Desktop metaphor: Zoom in using app-specific zoom controls or keyboard shortcuts (e.g., zoom dialogs, or $Ctrl$ + $"+"$ in many apps).
Touch metaphor: Zoom in by performing a two-finger pinch-out gesture on the image or content.
These zoom methods illustrate how the same action (zoom) is realized differently under different metaphors, reinforcing how metaphors guide interaction.