Difference Syntax Trees for Characterising Student in Programming Course

The Online Judge System (OJS) is well-used in programming courses at universities or for self-learning. The system compiles and executes a set of source codes submitted in response to an assignment and automatically grades them by comparing the output results and expectations. In university programming courses, especially courses for beginners, students repeatedly modify and submit source code until they receive a 100-point score. The OJS stores every source code until each student gets 100 points on an assignment; the differences through the first to last submissions contain helpful information to estimate students' understanding of syntax or learning units in the course. In this study, the authors propose difference flow, a series of syntax trees extracted from the differences between the final submission and every previous one. The difference flow contains the node where the difference with the 100-point source code and each parent node; hence, its features (such as the count of each syntax node throughout the flow) may indicate the students' understanding.