Online Computer Terms Dictionary - D

drag and drop

A common method for manipulating files (and sometimes text) under a graphical user interface or WIMP environment. The user moves the pointer over an icon representing a file and presses a mouse button. He holds the button down while moving the pointer (dragging the file) to another place, usually a directory viewer or an icon for some application program, and then releases the button (dropping the file). The meaning of this action can often be modified by holding certain keys on the keyboard at the same time.

Some systems also use this technique for objects other than files, e.g. portions of text in a word processor.

The biggest problem with drag and drop is does it mean "copy" or "move"? The answer to this question is not intuitively evident, and there is no consensus for which is the right answer. The same vendor even makes it move in some cases and copy in others. Not being sure whether an operation is copy or move will cause you to check very often, perhaps every time if you need to be certain. Mistakes can be costly. People make mistakes all the time with drag and drop. Human computer interaction studies show a higher failure rate for such operations, but also a higher "forgiveness rate" (users think "silly me") than failures with commands (users think "stupid machine"). Overall, drag and drop took some 40 times longer to do than single-key commands.

[Erik Naggum <erik@naggum.no>]

drag-n-drop

<spelling> Stupid spelling of drag and drop.

(1996-12-13)

DRAGON

1. An Esprit project aimed at providing effective support to reuse in real-time distributed Ada application programs.

2. An implementation language used by BTI Computer Systems.

E-mail: Pat Helland <helland@hal.com>.

[Jargon File]

(1994-12-08)

dragon

[MIT] A program similar to a daemon, except that it is not invoked at all, but is instead used by the system to perform various secondary tasks. A typical example would be an accounting program, which keeps track of who is logged in, accumulates load-average statistics, etc. Under ITS, many terminals displayed a list of people logged in, where they were, what they were running, etc., along with some random picture (such as a unicorn, Snoopy or the Enterprise), which was generated by the "name dragon". Use is rare outside MIT, under Unix and most other operating systems this would be called a "background demon" or daemon. The best-known Unix example of a dragon is cron. At SAIL, they called this sort of thing a "phantom".

[Jargon File]

Dragon Book

<publication> The classic text "Compilers: Principles, Techniques and Tools", by Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman (Addison-Wesley 1986; ISBN 0-201-10088-6). So called because of the cover design featuring a dragon labelled "complexity of compiler design" and a knight bearing the lance "LALR parser generator" among his other trappings. This one is more specifically known as the "Red Dragon Book" (1986); an earlier edition, sans Sethi and titled "Principles Of Compiler Design" (Alfred V. Aho and Jeffrey D. Ullman; Addison-Wesley, 1977; ISBN 0-201-00022-9), was the "Green Dragon Book" (1977). (Also "New Dragon Book", "Old Dragon Book".) The horsed knight and the Green Dragon were warily eying each other at a distance; now the knight is typing (wearing gauntlets!) at a terminal showing a video-game representation of the Red Dragon's head while the rest of the beast extends back in normal space.

See also book titles.

(1996-12-03)

DRAGOON

<language> A distributed, concurrent, object-oriented Ada-based language developed in the Esprit DRAGON project by Colin Atkinson at Imperial College in 1989 (Now at University of Houston, Clear Lake). DRAGOON supports object-oriented programming for embeddable systems and is presently implemented as an Ada preprocessor.

["Object-Oriented Reuse, Concurrency and Distribution: An Ada-Based Approach", C. Atkinson, A-W 1991, ISBN 0-2015-6-5277].

(1999-11-22)