Oscar Nierstrasz

Universität Bern | UniBe · Institute of Computer Science

Moldable development supports decision-making by making software systems explainable. This is done by making it cheap to add numerous custom tools to your software, turning it into a live, explorable domain model. Based on several years of experience of applying moldable development to both open-source and industrial systems, we have identified sev...

GitHub Actions (GA) is an orchestration platform that streamlines the automatic execution of software engineering tasks such as building, testing, and deployment. Although GA workflows are the primary means for automation, according to our experience and observations, human intervention is necessary to correct defects, update dependencies, or refac...

Debugging is hard. Interactive debuggers are mostly the same. They show you a stack, a way to sample the state of the stack, and, if the debugger is live, a way to step through execution. The standard interactive debugger for a general-purpose programming language provided by a mainstream IDE mostly offers a low-level interface in terms of generic...

Software systems should be explainable, that is, they should help us to answer questions while exploring, developing or using them. Textual documentation is a very weak form of explanation, since it is not causally connected to the code, so easily gets out of date. Tests, on the other hand, are causally connected to code, but they are also a weak f...

Code comments are important artifacts in software systems and play a paramount role in many software engineering (SE) tasks related to maintenance and program comprehension. However, while it is widely accepted that high quality matters in code comments just as it matters in source code, assessing comment quality in practice is still an open proble...

Code comments are important artifacts in software systems and play a paramount role in many software engineering (SE) tasks related to maintenance and program comprehension. However, while it is widely accepted that high quality matters in code comments just as it matters in source code, assessing comment quality in practice is still an open proble...

With behavior-driven development (BDD), domain experts describe system behavior and desired outcomes through natural language-like sentences, e.g., using the Gherkin language. BDD frameworks partially convert the content of Gherkin specifications into executable test code. Previous studies have reported several issues with the current BDD practice,...

We propose a tool, called FuzzingDriver, to generate dictionary tokens for coverage-based greybox fuzzers (CGF) from the codebase of any target program. FuzzingDriver does not add any overhead to the fuzzing job as it is run beforehand. We compared FuzzingDriver to Google dictionaries by fuzzing six open-source targets, and we found that FuzzingDri...

HTTP headers are commonly used to establish web communications, and some of them are relevant for security. However, we have only little information about the usage and support of security-relevant headers in mobile applications. We explored the adoption of such headers in mobile app communication by querying 9,714 distinct URLs that were used in 3...

IT professionals have no simple tool to create phishing websites and raise the awareness of users. We developed a prototype that can dynamically mimic websites by using enriched screenshots, which requires no additional programming experience and is simple to set up. The generated websites are functional and remain up-to-date. We found that 98% of...

Recent studies have shown that developers have difficulties in using cryptographic APIs, which often led to security flaws. We are interested to tackle this matter by looking into what types of problems exist in various crypto libraries. We manually studied 500 posts on Stack Overflow associated with 20 popular crypto libraries. We realized there a...

Context Previous studies have characterized code comments in various programming languages, showing how high quality of code comments is crucial to support program comprehension activities, and to improve the effectiveness of maintenance tasks. However, very few studies have focused on understanding developer practices to write comments. None of th...

Previous studies have shown that developers regularly seek advice on online forums to resolve their cryptography issues. We investigated whether users who are active in cryptography discussions also use cryptography in practice. We collected the top 1% of responders who have participated in crypto discussions on Stack Overflow, and we manually anal...

We surveyed 97 developers who had used cryptography in open-source projects, in the hope of identifying developer security and cryptography practices. We asked them about individual and company-level practices, and divided respondents into three groups (i.e., high, medium, and low) based on their level of knowledge. We found differences between the...

Code comments are the primary means to document implementation and facilitate program comprehension. Thus, their quality should be a primary concern to improve program maintenance. While much effort has been dedicated to detecting bad smells, such as clones in code, little work has focused on comments. In this paper we present our solution to detec...

Code comments are the primary means to document implementation and facilitate program comprehension. Thus, their quality should be a primary concern to improve program maintenance. While much effort has been dedicated to detecting bad smells, such as clones in code, little work has focused on comments. In this paper we present our solution to detec...

Assessing code comment quality is known to be a difficult problem. A number of coding style guidelines have been created with the aim to encourage writing of informative, readable, and consistent comments. However, it is not clear from the research to date which specific aspects of comments the guidelines cover (e.g., syntax, content, structure). F...

Code comments are important for program comprehension, development, and maintenance tasks. Given the varying standards for code comments, and their unstructured or semi-structured nature, developers get easily confused (especially novice developers) about which convention(s) to follow, or what tools to use while writing code documentation. Thus, th...

Prior research has shown that cryptography is hard to use for developers. We aim to understand what cryptography issues developers face in practice. We clustered 91954 cryptography-related questions on the Stack Overflow website, and manually analyzed a significant sample (i.e., 383) of the questions to comprehend the crypto challenges developers c...

[Background] Web communication is universal in cyberspace, and security risks in this domain are devastating. [Aims] We analyzed the prevalence of six security smells in mobile app servers, and we investigated the consequence of these smells from a security perspective. [Method] We used an existing dataset that includes 9714 distinct URLs used in 3...

Most software maintenance and evolution tasks require developers to understand the source code of their software systems. Software developers usually inspect class comments to gain knowledge about program behavior, regardless of the programming language they are using. Unfortunately, (i) different programming languages present language-specific cod...

Most software maintenance and evolution tasks require developers to understand the source code of their software systems. Software developers usually inspect class comments to gain knowledge about program behavior, regardless of the programming language they are using. Unfortunately, (i) different programming languages present language-specific cod...

[Background] Previous research has shown that developers commonly misuse cryptography APIs. [Aim] We have conducted an exploratory study to find out how crypto APIs are used in open-source Java projects, what types of misuses exist, and why developers make such mistakes. [Method] We used a static analysis tool to analyze hundreds of open-source Jav...

The ubiquity of smartphones, and their very broad capabilities and usage, make the security of these devices tremendously important. Unfortunately, despite all progress in security and privacy mechanisms, vulnerabilities continue to proliferate. Research has shown that many vulnerabilities are due to insecure programming practices. However, each st...

Previous studies have characterized code comments in different programming languages. However, very few studies have focused on the analysis of the information embedded in code comments. None of them compared the developer's practices to write the comments to the standard guidelines and analyzed these characteristics in the Pharo Smalltalk environm...

We studied the web permission API dialog box in popular mobile and desktop browsers, and found that it typically lacks measures to protect users from unwittingly granting web permission when clicking too fast. We developed a game that exploits this issue, and tricks users into granting webcam permission. We conducted three experiments, each with 40...

Factors such as app stores or platform choices heavily affect functional and non-functional mobile app requirements. We surveyed 45 companies and interviewed ten experts to explore how factors that impact mobile app requirements are understood by requirements engineers in the mobile app industry. We observed a lack of knowledge in several areas. Fo...

Research has shown that cryptographic APIs are hard to use. Consequently, developers resort to using code examples available in online information sources that are often not secure. We have developed a web platform, named CryptoExplorer, stocked with numerous real-world secure and insecure examples that developers can explore to learn how to use cr...

Web communication has become an indispensable characteristic of mobile apps. However, it is not clear what data the apps transmit, to whom, and what consequences such transmissions have. We analyzed the web communications found in mobile apps from the perspective of security. We first manually studied 160 Android apps to identify the commonly-used...

Android Inter-Component Communication (ICC) is complex, largely unconstrained, and hard for developers to understand. As a consequence, ICC is a common source of security vulnerability in Android apps. To promote secure programming practices, we have reviewed related research, and identified avoidable ICC vulnerabilities in Android-run devices and...

Although many tools have been presented in the research literature of software visualization, there is little evidence of their adoption. To choose a suitable visualization tool, practitioners need to analyze various characteristics of tools such as their supported software concerns and level of maturity. Indeed, some tools can be prototypes for wh...

Previous research has shown that crypto APIs are hard for developers to understand and difficult for them to use. They consequently rely on unvalidated boilerplate code from online resources where security vulnerabilities are common. We analyzed 2,324 open-source Java projects that rely on Java Cryptography Architecture (JCA) to understand how cryp...

The pivotal role of testing in high-quality software production has driven a significant effort in evaluating and assessing testing practices. We explore the state of testing in a large industrial project over an extended period. We study the interplay between bugs in the project and its test cases, and interview developers and stakeholders to unco...

Developers are usually unaware of the impact of code changes to the performance of software systems. Although developers can analyze the performance of a system by executing, for instance, a performance test to compare the performance of two consecutive versions of the system, changing from a programming task to a testing task would disrupt the dev...

[Context and Motivation] Mobile apps are crucial for many businesses. Their reach and impact on the end users and on the business in return demands that requirements are elicited carefully and properly. Traditional requirements elicitation techniques may not be adequate in the mobile apps domain. [Question/problem] Researchers have proposed numerou...

Several usability issues (i.e., navigation, occlusion, selection, and text readability) affect the few 3D visualizations proposed to support developers on software engineering tasks. We observe that most 3D software visualizations are displayed on a standard computer screen, and hypothesize that displaying them in immersive augmented reality can he...

Gamification of software engineering tasks improve developer engagement, but has been limited to mechanisms such as points and badges. We believe that a tool that provides developers an interface analogous to computer games can represent the gamification of software engineering tasks more effectively via software visualization. We introduce CityVR...

Many visualizations have proven to be effective in supporting various software related tasks. Although multiple media can be used to display a visualization, the standard computer screen is used the most. We hypothesize that the medium has a role in their effectiveness. We investigate our hypotheses by conducting a controlled user experiment. In th...

Bug prediction is the process of training a machine learning model on software metrics and fault information to predict bugs in software entities. While feature selection is an important step in building a robust prediction model, there is insufficient evidence about its impact on predicting the number of bugs in software systems. We study the impa...

Virtual application stores for mobile platforms contain many malign and benign applications that exhibit security issues, such as the leaking of sensitive data. In recent years, researchers have proposed a myriad of techniques and tools to detect such issues automatically. However, it is unclear how these approaches perform compared to each other....

Although software developers are usually reluctant to use static analysis to detect issues in their source code, our automatic just-in-time static analysis assistant was integrated into an Integrated Development Environment, and was evaluated positively by its users. We conducted interviews to understand the impact of the tool on experienced develo...

Parser combinators offer a universal and flexible approach to parsing. They follow the structure of an underlying grammar, are modular, well-structured, easy to maintain, and can recognize a large variety of languages including context-sensitive ones. However, these advantages introduce a noticeable performance overhead mainly because the same powe...

Background: Bug prediction helps developers steer maintenance activities towards the buggy parts of a software. There are many design aspects to a bug predictor, each of which has several options, i.e., software metrics, machine learning model, and response variable. Aims: These design decisions should be judiciously made because an improper choice...

Concurrency issues are inherently harder to identify and fix than issues in sequential programs, due to aspects like indeterminate order of access to shared resources and thread synchronisation. Live debuggers are often used by developers to gain insights into the behaviour of concurrent programs by exploring the call stacks of threads. Nevertheles...

Abundant studies have shown that visualization is advantageous for software developers, yet adopting visualization during software development is not a common practice due to the large effort involved in finding an appropriate visualization. Developers require support to facilitate that task. Among 368 papers in SOFTVIS/VISSOFT venues, we identify...

Object-oriented programming aims to facilitate navigation between domain concepts and the code that addresses those domains by enabling developers to directly model those domain concepts in the code. To make informed decisions, developers then formulate detailed and domain-specific questions about their systems in terms of domain concepts and use t...

Most static analyzers are monolithic applications that define their own ways to analyze source code and present the results. Therefore aggregating multiple static analyzers into a single tool or integrating a new analyzer into existing tools requires a significant amount of effort. Over the last few years, we cultivated Renraku --- a static analysi...

Exception handling allows developers to deal with abnormal situations that disrupt the execution flow of a program. There are mainly three types of exceptions: standard exceptions provided by the programming language itself, custom exceptions defined by the project developers, and third-party exceptions defined in external libraries. We conjecture...

The lack of static type information is one of the main obstacles to program comprehension in dynamically-typed languages. While static type inference algorithms try to remedy this problem, they usually suffer from the problem of false positives or false negatives. In order to partially compensate for the lack of static type information, a common pr...

Duck typing provides a way to reuse code and allow a developer to write more extensible code. At the same time, it scatters the implementation of a functionality over multiple classes and causes difficulties in program comprehension. The extent to which duck typing is used in real programs is not very well understood. We report on a preliminary stu...

Programming languages use exceptions to handle abnormal situations during the execution of a program. While programming languages often provide a set of standard exceptions , developers can further create custom exceptions to capture relevant data about project-and domain-specific errors. We hypothesize that, given their usefulness, custom exceptio...

Bug prediction is a technique that strives to identify where defects will appear in a software system. Bug prediction employs machine learning to predict defects in software entities based on software metrics. These machine learning models usually have adjustable parameters, called hyperparameters, that need to be tuned for the prediction problem a...

Bug prediction has been a hot research topic for the past two decades, during which different machine learning models based on a variety of software metrics have been proposed. Feature selection is a technique that removes noisy and redundant features to improve the accuracy and generalizability of a prediction model. Although feature selection is...

Software systems involve many different kinds of domain-specific and interrelated software entities. A common strategy employed by developers to deal with this reality is to perform exploratory investigations by means of searching. Nevertheless, most integrated development environments (IDEs) support searching through generic and disconnected searc...

Although dynamically typed languages allow developers to be more productive in writing source code, their lack of in- formation about types of variables is one of the main obstacles during program comprehension. Static type information helps developers to decrease software maintenance time. Inference of types of variables requires complex algorithm...

Software visualization can be very useful for answering complex questions that arise in the software development process. Although modern visualization engines offer expressive APIs for building such visualizations, developers often have difficulties to (1) identify a suitable visualization technique to answer their particular development question,...