Aletta Nylén

Forward Reachability Analysis of Timed Petri Nets

We consider verification of safety properties for concurrent real-timed systems modelled as timed Petri nets, by performing symbolic forward reachability analysis. We introduce a formalism, called region generators for representing sets of markings of timed Petri nets. Region generators characterize downward closed sets of regions, and provide exact abstractions of sets of reachable states with respect to safety properties. We show that the standard operations needed for performing symbolic reachability analysis are computable for region generators. Since forward reachability analysis is necessarily incomplete, we introduce an acceleration technique to make the procedure terminate more often on practical examples. We have implemented a prototype for analyzing timed Petri nets and used it to verify a parameterized version of Fischer’s protocol and a producer-consumer protocol. We also used the tool to extract finite-state abstractions of these protocols.

Professional communication skills for engineering professionals

Oral and written communication proficiency is an important professional skill for engineering graduates. However, developing these skills is often poorly integrated into the engineering curriculum. We present a three year integrated approach to developing professional competence in oral and written communication, which has been implemented in the IT engineering program at a Swedish research university. In the paper we describe the educational approach, the nature of assessment items and measures taken to ensure progressive skills development in order to ensure that graduates emerge with fully fledged communications skills. The goal of the paper is to describe a successful model for professional skills development, and to encourage a continuing dialogue on how to best equip students with communication skills for professional practice.

SAT-Solving the Coverability Problem for Petri Nets

Net unfoldings have attracted great attention as a powerful technique for combating state space explosion in model checking, and have been applied to verification of finite state systems including 1-safe (finite) Petri nets and synchronous products of finite transition systems. Given that net unfoldings represent the state space in a distributed, implicit manner the verification algorithm is necessarily a two step process: generation of the unfolding and reasoning about it. In his seminal work McMillan (K.L. McMillan, Symbolic Model Checking. Kluwer Academic Publishers, 1993) showed that deadlock detection on unfoldings of 1-safe Petri nets is NP-complete. Since the deadlock problem on Petri nets is PSPACE-hard it is generally accepted that the two step process will yield savings (in time and space) provided the unfoldings are small.In this paper we show how unfoldings can be extended to the context of infinite-state systems. More precisely, we show how unfoldings can be constructed to represent sets of backward reachable states of unbounded Petri nets in a symbolic fashion. Furthermore, based on unfoldings, we show how to solve the coverability problem for unbounded Petri nets using a SAT-solver. Our experiments show that the use of unfoldings, in spite of the two-step process for solving coverability, has better time and space characteristics compared to a traditional reachability based implementation that considers all interleavings for solving the coverability problem.

Unfoldings of Unbounded Petri Nets

Net unfoldings have attracted much attention as a powerful technique for combating state space explosion in model checking. The method has been applied to verification of 1-safe (finite) Petri nets, and more recently also to other classes of finite-state systems such as synchronous products of finite transition systems. We show how unfoldings can be extended to the context of infinite-state systems. More precisely, we apply unfoldings to get an efficient symbolic algorithm for checking safety properties of unbounded Petri nets. We demonstrate the advantages of our method by a number of experimental results.

Understanding initial undergraduate expectations and identity in computing studies

ABSTRACT There is growing appreciation of the importance of understanding the student perspective in Higher Education (HE) at both institutional and international levels. This is particularly important in Science, Technology, Engineering and Mathematics subjects such as Computer Science (CS) and Engineering in which industry needs are high but so are student dropout rates. An important factor to consider is the management of students’ initial expectations of university study and career. This paper reports on a study of CS first-year students’ expectations across three European countries using qualitative data from student surveys and essays. Expectation is examined from both short-term (topics to be studied) and long-term (career goals) perspectives. Tackling these issues will help paint a picture of computing education through students’ eyes and explore their vision of its and their role in society. It will also help educators prepare students more effectively for university study and to improve the student experience.

Teaching and learning with MOOCs: computing academics' perspectives and engagement

During the past two years, Massive Open Online Courses (MOOCs) have created wide interest in the academic world raising both enthusiasm for new opportunities for universities and many concerns for the future of university education. The discussion has mainly appeared in non-scientific forums, such as magazine articles, columns and blogs, making it difficult to judge wider opinions within academia. To collect more rigorous data we surveyed teachers, researchers, and academic managers on their opinions and experiences of MOOCs. In this paper, we present our analysis of responses from the computer science academic community (n=137). Their feelings about MOOCs are highly mixed. Content analysis of open-ended questions revealed that the most often mentioned positive aspects included affordances of MOOCs, freedom of time and location for studying, and the possibility to experience teaching from top-level international teachers/experts. The most common negative aspects included concerns about pedagogical designs of MOOCs, assessment practices, and lack of interaction with the teacher. About half the respondents claimed they had not changed their teaching as a result of MOOCs, a small number used MOOCs as learning resources and very few were engaging with MOOCs in any significant way.

A critical analysis of trends in student-centric engineering education and their implications for learning

Student-centric education has emerged as a dominant aspect of Higher Education policy over the last two decades. Much has been written about the benefits of student active educational approaches, and applied educational research, for instance the meta-study of Hattie, places emphasis on student-centric learning practices that enhance achieved learning outcomes. Most existing studies have been evaluations of single courses. In contrast this study focusses on the complete study context of the learner, who typically is in the situation of reading two or three courses simultaneously. Our primary goal in this paper is to explore potential challenges as we attempt to scale up active learning to encompass the full curricula. We use a mixture of interview and survey data collected from staff, combined with course schedules and student input to explore some of the potential implications of mandating a student-centric approach over an entire curriculum.

Enhanced learning by promoting engineering competencies

An engineering graduate needs to master a number of important skills: problem solving, critical thinking, communication, collaboration, etc. In this paper we describe how a course in computer security, taught in the Computer and Information Engineering programme at Uppsala University, has been developed over a period of three years. The aim is to better develop the engineering competencies of students, improving their understanding of course contents, training their ability to reflect on it, and to apply their knowledge when facing realistic problems. The course is designed to activate students, based on practical labs and theoretical tasks which are solved in groups. The student reports are assessed at seminars, where the solutions are presented orally, peer-reviewed and discussed. The seminars encourage and reward activities at the higher levels of taxonomies such as Blooms. The results of the development, based on a CEQ-based course evaluation, indicate that students take a deeper approach to learning. They develop their problem-solving skills to a high degree, appreciate the practical solving of open-ended problems, and take responsibility for collaborative learning. Their overall satisfaction with the course is quite high, despite indications that they find the workload high.

Open-ended projects opened up — aspects of openness

One of the most important areas of competence for professional engineers is the ability to function well in project work, in particular they need to be able to efficiently solve open-ended problems in different collaborative settings. The development of this ability is however not prominent in engineering education despite numerous authors suggesting open-ended problems as a pedagogical tool to promote development of collaborative problem solving competence by including elements of group or project work in courses. In our own long experience of using open-ended problems in collaborative student projects, we have identified a lack of systematic progression in learning outcomes and skill development. We see this as a major obstacle for fully exploiting the potentials of using open-ended problems as an educational tool. We present a framework that provides a structured view of challenges related to openness that students can encounter in educational projects and that has an impact on the overall complexity of the project. We argue that there are different categories of openness to consider when designing educational settings based on open-ended projects. The categories addressed in this paper are: Character of the problems addressed. Character of the teams. Time constraints. Faculty involvement. External factors. Aspects of openness in the different categories are presented and related to professional engineering competencies. Furthermore, it is discussed how variations in project complexity can be accomplished by variations within the aspects and combinations of aspects. In particular, the framework addresses development and progression of professional competencies.

Multidimensional analysis of creative coding MOOC forums: a methodological discussion

The emergence of Massive Open Online Courses (MOOCs) in higher education has led to new variations in the social and educational interactions that students have with their peers and teachers. In this paper, we focus on methodological issues and discuss different options for analysis frameworks for forum posts in MOOCs. The ultimate aim of our ongoing research is to understand how factors relating to interactions and discussions may lead to better learning outcomes in programming courses. We performed a multidimensional analysis using existing frameworks for a small data set extracted from a larger data pool from a Creative Coding MOOC. Based on this pilot study, we discuss how different analysis approaches contribute to gaining a holistic understanding of online interactions. We found the need to redefine existing frameworks for the specific analysis of MOOC discussions and in particular, for computer science focused discussions. We conclude by highlighting some of the themes and challenges we are expecting in our future work, such as, how to automate data analysis of MOOC discussions.