! Social Computing Ethnography of a Print Shop

ion Software systems are built from abstractions. The extent to which abstraction is fundamental to software systems can be hard to explain to someone who hasn’t built them; while to someone who has, it can be so ubiquitous as to have become invisible. But the very essence of software system design is the manipulation, combination, and creation of abstractions. User interfaces offer us abstractions in the form of generic user interface components or “widgets” such as menus, buttons, labels, and scroll bars. Widgets are arranged to form an interface by a programmer, who manipulates them in the form of objects with certain definable and controllable characteristics (such as color, size, or font). These objects are abstractions in the traditional software sense—entities whose essence lies in the range of manipulations they allow, and whose inner workings can be ignored as long as the external constraints are maintained. The very notion of “object” in a software system is itself an abstraction, exposing the “essence” of the object (that is, exposing the ways in which it can be examined and manipulated) while hiding a range of details of implementation (such as where the object resides in system memory, or how the details of its internal components will be represented). Object systems are themselves implemented on top of programming languages, which are abstractly manipulated by other programs to yield machine-language representations, sequences of operations in the instruction set of whatever processor will run the program. Here, again, we encounter abstractions. The instruction set is an abstraction that hides a variety of possible implementations (as we see when “clone” processors appear using completely different technology to implement the same instructions, or when a manufacturer produces a new generation of processors that are “backward compatible” with last year’s instruction set). Similarly, the notion of a uniform processor abstracts away the specific details of each individual device. Software systems, in other words, constitute a tower of dour_ch03.fm Page 81 Thursday, May 24, 2001 11:40 AM