Software Engineering and Programming Languages
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Dhrystone: a synthetic systems programming benchmark
Reflecting current data on the use of programming language constructs in systems programming, a synthetic benchmark is constructed based on the distribution appearing in the data. The benchmark executes 100 Ada statements that are balanced in terms of the distribution of statement types, data types, and data locality. Pascal and C versions of the benchmark are discussed.
Building a user-derived interface
Many human-computer interfaces are designed with the assumption that the user must adapt to the system, that users must be trained and their behavior altered to fit a given interface. The research presented here proceeds from the alternative assumption: Novice behavior is inherently sensible, and the computer system can be made to adapt to it. Specifically, a measurably easy-to-use interface was built to accommodate the actual behavior of novice users. Novices attempted an electronic mail task using a command-line interface containing no help, no menus, no documentation, and no instruction. A hidden operator intercepted commands when necessary, creating the illusion of an interactive session. The software was repeatedly revised to recognize users' new commands; in essence, the interface was derived from user behavior. This procedure was used on 67 subjects. The first version of the software could recognize only 7 percent of all the subjects' spontaneously generated commands; the final version could recognize 76 percent of these commands. This experience contradicts the idea that user input is irrelevant to the design of command languages. Through careful observation and analysis of user behavior, a mail interface unusable by novices evolved into one that let novices do useful work within minutes.
Since the mid-1970s, the U.S. Department of Defense has been laying the groundwork for a major new computer language that may substantially displace FORTRAN and COBOL in the years ahead. With Ada just now starting to be used, Communications felt it would be timely to conduct an interview with Jean Ichbiah, the principal designer of this new language. Ichbiah discusses the evolution of Ada, evaluates its success so far, and speculates on its future.
Architecture of the space shuttle primary avionics software system
PASS, perhaps the most complex flight computer program ever developed, epitomizes the benefits to be gained by establishing a well-structured system architecture at the front end of the development process
A software design method for real-time systems
DARTS—a design method for real-time systems—leads to a highly structured modular system with well-defined interfaces and reduced coupling between tasks.
Improved interpretation of UNIX-like file names embedded in data
When the data processed by a program span several files, the common practice of including file names as data in some of the files leads to difficulties in moving or sharing that data. In systems using tree structured directories, this problem can be solved by making a syntactic distinction between absolute and relative file names.
Memory occupancy patterns in garbage collection systems
Some programming languages and computer systems use dynamic memory allocation with garbage collection. It would be useful to understand how the utilization of memory depends on the stochastic parameters describing the size and life distributions of the cells. We consider a class of dynamic storage allocation systems which use a first-fit strategy to allocate cells and perform noncompacting garbage collections to recover free memory space when memory becomes fully occupied. A formula is derived for the expected number of holes (available cells) in memory immediately following a garbage collection which specializes to an analogue of Knuth's 'Fifty Percent' rule for nongarbage-collection systems. Simulations confirm the rule for exponentially distributed cell lifetimes. Other lifetime distributions are discussed. The memory-size requirements for noncompacting garbage collection are also analyzed.
The EAS-E application development system: principles and language summary
EAS-E is based on the entity-attribute-set view of system description—a useful formalism for system modeling and planning even when programming is done in languages other than EAS-E.
Determinants of program repair maintenance requirements
Considerable resources are devoted to the maintenance of programs including that required to correct errors not discovered until after the programs are delivered to the user. A number of factors are believed to affect the occurrence of these errors, e.g., the complexity of the programs, the intensity with which programs are used, and the programming style. Several hundred programs making up a manufacturing support system are analyzed to study the relationships between the number of delivered errors and measures of the programs' size and complexity (particularly as measured by software science metrics), frequency of use, and age. Not surprisingly, program size is found to be the best predictor of repair maintenance requirements. Repair maintenance is more highly correlated with the number of lines of source code in the program than it is to software science metrics, which is surprising in light of previously reported results. Actual error rate is found to be much higher than that which would be predicted from program characteristics.
Pass-algorithms: a user validation scheme based on knowledge of secret algorithms
A superset of the secondary passwords technique, pass-algorithms provide enormous flexibility and ease of implementation and represent an attractive alternative to more costly systems security features and equipment. The method validates users who demonstrate knowledge of a secret algorithm rather than a password.
We are entering a new era in very high performance computing that will be dominated by parallel architectured systems. It is critical for the United States to maintain its leadership as this new era, with its broadened applications, evolves over the next decade. Toward this end the National Science Foundation sponsored a workshop in November 1983 to focus the collective strength of universities, industry, and government on projects for development of knowledge-intensive industries.
Reflections on software research
Can the circumstances that existed in Bell Labs that nurtured the UNIX project be produced again?
To what extent should one trust a statement that a program is free of Trojan horses? Perhaps it is more important to trust the people who wrote the software.
Training wheels in a user interface
New users of high-function application systems can become frustrated and confused by the errors they make in the early stages of learning. A training interface for a commercial word processor was designed to make typical and troublesome error states “unreachable,” thus eliminating the sources of some new-user learning problems. Creating a training environment from the basic function of the system itself afforded substantially faster learning coupled with better learning achievement and better performance on a comprehension post-test. A control group spent almost a quarter of their time recovering from the error states that the training interface blocked off. We speculate on how this training strategy might be refined, and more generally, on how function should be organized in a user interface.
Data that are missing, lost, or incomplete can be very significant in certain situations. Programs and languages need to be able to identify and manage such data effectively.
Visibility aspects of programmed dynamic data structures
Unlike static structures, dynamic Pascal-like data structures often suffer visibility problems due to the unrestricted use of the general pointer mechanism. By classifying these structures and identifying the different kinds of pointers, a methodology is proposed for achieving improved visibility.
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