A programming system is the user interface between the programmer and the computer. Programming is a notoriously difficult activity, and some of this difficulty can be attributed to the user interface as opposed to other factors. Historically, the designs of programming languages and tools have not emphasized usability. This paper describes the process we used to design HANDS, a new programming system for children that focuses on usability, where HCI knowledge, principles, and methods guided all design decisions. The features of HANDS are presented along with their motivations from prior empirical research on programmers and new studies conducted by the authors. HANDS is an event-based language that features a concrete model for computation, provides operators that match the

Abstract. There are more APIs than ever, and designing APIs that are usable by their target audience is difficult. Work at Microsoft has demonstrated that running controlled usability studies with participants from different personas and analyzing the results of these studies using the cognitive dimensions framework is effective at identifying and preventing usability problems in APIs. This paper presents a generalization of that technique in the form of usability studies of common API design choices. By studying a single design choice from multiple perspectives, we can generalize our results to any API that might be affected by the design choice. We show the feasibility of our approach with an initial study on whether or not to require constructor parameters, and present our current and planned work to study more API design choices. 1

The event-based style is increasingly common in modern end-user programming languages. Visual Basic, Macromedia’s Director, web scripting languages, as well as many recent novice-geared research prototypes such as

Designers are skilled at sketching and prototyping the look of interfaces, but to explore various behaviors (what the interface does in response to input) typically requires programming using Javascript, ActionScript for Flash, or other languages. In our survey of 259 designers, 86 % reported that the behavior is more difficult to prototype than the appearance. Often (78 % of the time), designing the behavior requires collaborating with developers, but 76 % of designers reported that communicating the behavior to developers was more difficult than the appearance. Other results include that annotations such as arrows and paragraphs of text are used on top of sketches and storyboards to explain behaviors, and designers want to explore multiple versions of behaviors, but today’s tools make this difficult. The results provide new ideas for future tools. 1.