Wilfred J. Hansen

Reading and writing with computers: a framework for explaining differences in performance

Several factors can influence the behavior of users as they read and write with computers. Recent research indicates that both quality and quantity depend upon page size, legibility, responsiveness and tangibility.

Measurement of program complexity by the pair: (Cyclomatic Number, Operator Count)

In a r e c e n t paper, McCabe [1976] i n t r o d u c e d the cyclomatic number of a programs flow graph as a measure of its complexity. Myers [1977] proposed an improved measure consisting o[ an interval with the original measure as its upperbound. I will argue below that--if two values are to be presented as a measure--it is preferable to couple a variation of the cyclomatic number with a measure o[ the prog~-ams express:ion complexity.

Enhancing documents with embedded programs: how Ness extends insets in the Andrew ToolKit

The problems of embedding programs in documents are sketched and the solutions adopted in the Ness component of the Andrew ToolKit are reviewed. A key question is the connection from user actions to program functions. Other questions include the appropriate level of programming language, its string-processing capabilities, and security.<<ETX>>

Why an Examination Was Slower On-Line than On Paper.

Although most interactive systems seem to facilitate user work, our system—an interactive examination system—increased the time required by as much as 100%. To explore this phenomenon we videotaped four students taking an exam interactively and on paper. Analysis showed the extra time went to system overhead, think time and trouble understanding what to do. We were able to explain the latter two categories as the result of four varieties of “uncertainty”. Evidence included changes in review behavior and working habits, hesitation before leaving a page and the “context switch” time required to recognize even a familiar image. With subsequent improvements the increased time has been largely eliminated.

The 1994 Visual Languages Comparison

Diverse visual languages have been proposed, implemented, and published; but each is demonstrated on problems chosen by its authors. To make a fair comparison, the 1994 Visual Languages Comparison project proposed a set of three problems and solicited solutions to these problems in various visual languages. Submissions arrived for one graphic rewriting system-ChemTrains-and four data flow languages-LabVIEW, Prograph, Show and Tell, and VisaVis.<<ETX>>

Introduction to user interface systems for HCI developers and researchers

User inte~ace systems (UIS) combine essential applications for compound documents with a toolkit for building new applications that inter-operate with the others. The essential applications-word processing, drawing editor, spread sheet, equation editor, image editor, electronic mail management, and so on-all support embedding of objects to create compound documents and can themselves all be embedded as objects in compound documents. When building new applications, the user draws the screen image with the drawing editor and selects components from among the applications or the objects in the toolkit. The earliest and most complete system at this time is the Andrew User Interface System, which will be used for examples during the tutorial. User Interface Systems challenge HCI workers to develop interface conventions that stretch harmoniously across the wide spectrum of applications. However, these same systems aid HCI work by simplifying construction of experimental interfaces and providing tools for evaluation of user behavior across multiple diverse applications.

Subsequence references: first-class values for substrings

Arrays of characters are a basic data type in many programming languages, but strings and substrings are seldom accorded first-class status as parameters and return values. Such status would enable a routine that calls a search function to readily access context on both sides of a return value. To enfranchise substrings, this paper describes a new data type for substrings as a special case of one for general subsequences. The key idea is that values are not sequences or references to positions in sequences, but rather references to subsequences. Primitive operations on the data type are constants, concatenation, and four new functions—base, start, next, and extent—which map subsequence references to subsequence references. This paper informally presents the data type, demonstrates its convenience for defining search functions, and shows how it can be concisely implemented. Examples are given in Ness, a language incorporating the new data type, which is implemented as part of the Andrew User Interface System.

The Andrew environment of development for development of educational computing

Abstract Andrew is being developed at Carnegie-Mellon University as an environment for computing by all members of the campus community. The system includes a file system, user interface software, and the CMU-Tutor facility for building instructional material. This demonstration focuses on the latter environment, showing how it provides excellent facilities for generating images and evaluating student responses to questions.

Graphic Editing of Structured Text

Emily, the system described in this paper, is an interactive syntax-controlled system for creation and manipulation of program texts. This system uses the syntax of the programming language to impose a tree structure on programs in the language. A program begins as a single non-terminal symbol. For each non-terminal Emily presents all the syntax rules that define replacements for that non-terminal. In general, the replacement string consists of characters and non-terminals. By selecting appropriate rules, the user builds the program he desires. Because the editor retains the tree structure of the text, the text can be manipulated in terms of its structural units. Emily can represent any structural element by a single identifier, so that the user can view his text at any level of complexity. As a hybrid of string and tree representations, this display technique provides a new way of looking at and thinking about programs.

Spiral development and evolutionary acquisition: the SEI-CSE workshop

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