In an article that was published in Byte magazine, Smith et al. (1982) describe the Xerox Star system and how its interface was designed.
The Star was very different from other personal computers of its time. It had more features than its predecessors and introduced new concepts of human computer interaction. Its design was driven by a small set of design principles or rules which made it user friendly and simple to understand. The consistent application of the principles made it possible for the users to apply their experience from one part of the system to another.
A pointing device called a "mouse"
The Star was based on the previous Xerox Alto computer. It had a 10 ½ by 13 ½ inch 72 dpi monitor, a pointing device called a “mouse” and a 10-megabits-per-second Ethernet connection. The Star was about three times as fast as the preceding Alto. To support its novel visual interface the Star also featured specially engineered hardware that made it possible.
The design team predicted, that all impressive office systems of the future would have bit-mapped displays, and that the memory cost would soon be insignificant enough, that they would be feasible even in home computers. Visual communication is effective, and it couldn't be exploited without graphics flexibility.
A ground breaking part of the design process was, that the designers started by defining a conceptual model of how the user would relate to the system. Hardware and software followed from this. The design team worked for two years before they wrote a single line of actual product software.
The designers employed a specific design methodology to create the Star. The process started with a task analysis, which involved establishing who the users are, what their goals are in performing the task, what information they use in performing it, what information they generate, and what methods they employ. The current task description offers a starting point for the design of a new task environment, or an interface metaphor, in which the user can work to accomplish the same goals as before.
The designers perceived the Xerox Alto as a sort of a prototype for the Star. Alto users had had several thousand work-years of experience with them over a period of eight years. The Alto was and is arguably one of the largest prototyping efforts ever. For the designers the concept of prototyping was to consciously create a version of the system that would inevitably be “thrown away”.
As a part of the process the designers created a simple classification of core concepts that can be seen as counterparts of sorts.
Following this classification, they incorporated the easy ones to the Star’s conceptual model and avoided the hard ones.
The main goals of the design process were:
- Familiar user's conceptual model
- Seeing and pointing versus remembering and typing
- What you see is what you get
- Universal commands
- Modeless interaction
- User tailorability
The desktop metaphor
The user’s conceptual model is the model the user acquires to explain the behaviour of the system. This system enables the user to understand and interact with the system. Through their design of Alto and Star the Xerox team gave birth to the desktop metaphor, or the “physical- office metaphor” as it is referred to in the article.
The icons of the Star, were concrete embodiments of physical objects and the users were encouraged to think of them in physical terms. The icons could be moved to arrange the desktop. Even messy Desktops were possible, just as in real life. This kind of an environment encourages the user to experiment, verify, and expand their understanding of the system.
In a complex system, it is often not possible to represent everything in terms of a single model. There may need to be more than one model, but the number of different user models in a system should be kept to a minimum.
A well-designed system makes everything relevant to a task visible on the screen. The idea is, that when everything being dealt with in a system is visible, the display relieves the load on the user’s short term memory by acting as a sort of a visual cache.
The Star also featured a WYSIWYG text editor that was a direct descendant of the Bravo editor, which was the first powerful WYSIWYG editor that was created for the Alto.
The Star had a set of “universal commands”: MOVE, COPY, DELETE, SHOW PROPERTIES, COPY PROPERTIES, AGAIN, UNDO, and HELP. Each them could be used throughout the system and performed the same way regardless of the type of object selected. These commands had separate keys in the Star’s keyboard. Such commands might seem obvious nowadays, but their selection at the time was a an important part of the design. These generic commands derived from fundamental computer science concepts that also underlie operations in programming languages. Much program manipulation of data structures involves moving or copying values from one data structure to another.
The icons of the Star were classified in practical manner into data icons and function icons. Data icons represented objects on which actions were performed, whereas function icons represented objects that performed actions. Data icons could be further divided into three subclasses: documents, folders, and record files. The Star’s function icons included for instance file drawers, in- and out-baskets, printers, floppy-disk drives, calculators and terminal emulators. Consistently anything that could be done to one data icon could be done to all, regardless of its type, size, or location.
A tradeoff often exists between easy novice use and efficient expert use. The Star’s design team tried to follow Alan Kay's maxim: "simple things should be simple; complex things should be possible". To achieve simplicity they pursued uniformity and consistency, and at the same time tried to minimize redundancy. Having two or more ways to do something increases the complexity without increasing the capabilities of a system.
Systems sometimes utilize modes when there are too few keys or not enough space for keys to represent all the available commands. One problem with modes is, if you don’t notice what mode the system is in, you may invoke different commands than what you had intended.
Commands in the Star took the form of noun-verb. The user would specify the object (the noun) and then invoke a command to manipulate it (the verb). Modifier keys of the keyboard can be thought of as modes. The command or control keys of modern keyboards put the keyboard to a function mode where you can call for copy, paste and a variety of other functions. The Star eliminated this type of basic modes by having completely separate keys for invoking these functions.
The authors recognized the most important factors affecting how prevalent computer usage would become in the 1980s as: “reduced cost, increased functionality, improved availability and servicing, and, perhaps most important of all, progress in user-interface design”. They saw user-interface design as an art, more than science. Often there is no one "right" answer and no scientific evidence to support one alternative over another, just intuition. In conclusion, they hoped that, by the end of the decade, user-interface design would be a more rigorous process. And one that they have contributed to.
Smith, D.C., Irby, C., Kimball, R. and Verplank, B. (1982) “Designing the STAR user interface”, Byte 7, 242-282