Kian L. Pokorny

Frances: a tool for understanding code generation

Compiler and programming language implementation courses are integral parts of many computer science curricula. However, the range of topics necessary to teach in such a course are difficult for students to understand and time consuming to cover. In particular, code generation is a confusing topic for students unfamiliar with low level target languages. We present Frances, a tool for helping students understand code generation and low level languages. The key idea is to graphically illustrate the relationships between high level language constructs and low level (assembly) language code. By illustrating these relationships, we take advantage of the students existing understanding of some high level language. We have used Frances in a compiler design course and received highly positive feedback. Students conveyed to us that Frances significantly helped them to understand the concepts necessary to implement code generation in a compiler project.

Uncertainty estimates in the fuzzy-product-limit estimator

The Fuzzy-Product-Limit Estimator (FPLE) is a method for estimating a survival curve and the mean survival time when very few data are available and a high proportion of the data are censored. Considering censored times as vague failure times, the censored values are represented by fuzzy membership functions that represent a belief of continued survival of the associated unit. Associated with any estimate is uncertainty. With the FPLE two distinct types of uncertainty exist in the estimate, the uncertainty, due to the randomness in the recorded times and the vague uncertainty in the failure of the censored units. This paper addresses the problem of providing confidence bounds and estimates of uncertainty for the FPLE. Several methods for estimating the vague uncertainty in the estimator are suggested. Among them are the use of Efrons Bootstrap that obtains a confidence interval of the FPLE to quantify random uncertainty and produces an empirical distribution that is used to quantify properties of the vague uncertainty. Also, a method to obtain a graphical representation of the random and vague uncertainties is developed. The new methods provide confidence intervals that quantify statistical uncertainty as well as the vague uncertainty in the estimates. Finally, results of simulations are provided to demonstrate the efficacy of the estimator and uncertainty in the estimates.

Fuzzy survival analysis of AIDS patients under ten years old in Hamadan-Iran

A common and critical issue in survival data analysis is the way in which censored data are handled. The Kaplan-Meier KM estimator is a frequently used statistical method in survival analysis that works well with censored data. In small sample sizes with heavy censoring the estimates of KM are not reliable, because the assumptions of KM estimator are violated. In this study, fuzzy logic is used to obtain more reliable estimates when standard statistical methods cannot be used. Data analyzed in this study were the survival times of six AIDS patients under ten years old. One of the patients died after 197 days and the others were censored, giving a censor rate of 83%. The fuzzy-product-limit estimator FPLE and a modified FPLE were used to analyze the data. Mean survival time was calculated and associated confidence interval was calculated along with a measure of the amount of “fuzzy information” used to obtain the estimates. In addition, one to ten year survival rates estimated by the KM, FPLE and proposed methods are presented. The result of the simulations showed that the fuzzy methods with few and highly censored data provide more reasonable results than the standard statistical method.

EMPIRICAL FUZZY ESTIMATE OF THE SURVIVAL CURVE

In this paper, a computational system is developed that estimates a survival curve and a point estimate when very few data are available and a high proportion of the data are censored. Standard sta...

Creating a Computer Simulator as a CS1 Student Project

This paper presents experiences with creating a computer simulator as a student project in a CS1 course. Each student writes the simulator using C++ during the last ten weeks of the course. The project consists of a simulated memory, and simple CPU simulator including a machine language. Additionally, students implement an assembly language and a simple high-level language with associated compiler. The course has no programming prerequisite and can be taken to fulfill a general education requirement or as the first course for students majoring in computer science or information systems. Integrating such a project in an entry level course has a number of benefits as well as challenges. The project acts as a vehicle that engages students in a breadth of computer science topics, leading into discussions of theoretical considerations, languages, and computing devices. The project components provide an active learning environment. Students are introduced to numbering systems, number conversions, and numeric representations. The computer architecture components include introductions to main memory, CPU, and memory access techniques. The transition from and motivations for, the utilization of machine languages, assembly languages and high-level languages are demonstrated with the implementation of the project. Beginning students are given opportunity to practice programming and problem solving on a project of significant complexity. The biggest challenge is organization. Management of such a project requires a well-defined plan.

Frances: A Tool for Understanding Computer Architecture and Assembly Language

Students in all areas of computing require knowledge of the computing device including software implementation at the machine level. Several courses in computer science curricula address these low-level details such as computer architecture and assembly languages. For such courses, there are advantages to studying real architectures instead of simplified examples. However, real architectures and instruction sets introduce complexity that makes them difficult to grasp in a single semester course. Visualization techniques can help ease this burden, unfortunately existing tools are often difficult to use and consequently difficult to adopt in a course where time is already limited. To solve this problem, we present Frances. Frances graphically illustrates key differences between familiar high-level languages and unfamiliar low-level languages and also illustrates how familiar high-level programs behave on real architectures. Key to this tool is that we use a simple Web interface that requires no setup, easing course adoption hurdles. We also include several features that further enhance its usefulness in a classroom setting. These features include graphical relationships between high-level code and machine code, clearly illustrated step-by-step machine state transitions, color coding to make instruction behavior clear, and illustration of pointers. We have used Frances in courses and performed experimental evaluation. Our experiences with Frances in the classroom demonstrate its usability. Most notably, in our experimental setting, students with no computer architecture course experience were able to complete lessons using Frances with no guidance.