Wardah Mahmood

Features are commonly used to describe the functional and non-functional characteristics of software. Especially agile development methods, such as SCRUM, FDD, or XP, use features to plan and manage software development. Features are often the main units of software reuse, communication, and configuration, abstracting over code details. Especially in the age of generative AI, where feature requirements are specified as prompts and substantial code is cloned, codebases are becoming increasingly complex and redundant. This requires raising the level of abstraction at which we manage and evolve software systems. However, effectively using features requires knowing their precise locations within codebases, which is especially challenging when they are scattered across the codebase. Once implemented, the knowledge about a feature’s location quickly deteriorates when the software evolves or development teams change, requiring expensive recovery of features. This decades-old problem is known as the feature-location or concept assignment problem in software engineering, which researchers have— unsuccessfully over decades—tried to address with automated feature-location recovery techniques. The problem lies in the common belief that recording and maintaining feature locations during development is laborious and error-prone. In this study, we argue to the contrary. We hypothesize that such information can be effectively embedded into codebases, and that the arising costs will be amortized by the benefits of this information. We validated this hypothesis in a simulation study with three subjects systems: a smaller open source system, a large commercial firmware system, and an open source mobile app. We designed a lightweight code annotation technique and simulated its use as if annotations had been added, maintained, and exploited during the original development. We identified evolution patterns and measured the cost and benefit of these annotations. Our results show that not only the cost of adding annotations, but also that of maintaining them is negligible compared to the development and maintenance costs of the actual code. Embedding the annotations into the codebase significantly reduced their maintenance effort, because they naturally co-evolved with the code. The annotations provided a benefit for feature-related maintenance tasks, such as feature cloning or merging the clones into an integrated codebase, that exceeded the costs of using them.

Almost any software system needs to exist in multiple variants. While branching or forking-a.k.a. clone & own—are simple and inexpensive strategies, they do not scale well with the number of variants created. Software platforms—a.k.a. software product lines—scale and allow to derive variants by selecting the desired features in an automated, tool-supported process. However, product lines are difficult to adopt and to evolve, requiring mechanisms to manage features and their implementations in complex codebases. Such systems can easily have thousands of features with intricate dependencies. Feature models have arguably become the most popular notation to model and manage features, mainly due to their intuitive, tree-like representation. Introduced more than 30 years ago, thousands of techniques relying on feature models have been presented, including model configuration, synthesis, analysis, and evolution techniques. However, despite many success stories, organizations still struggle with adopting software product lines, limiting the usefulness of such techniques. Surprisingly, no modeling process exists to systematically create feature models, despite them being the main artifact of a product line. This challenges organizations, even hindering the adoption of product lines altogether. We present FM-PRO, a process to engineer feature models. It can be used with different adoption strategies for product lines, including creating one from scratch ( pro-active adoption ) and re-engineering one from existing cloned variants ( extractive adoption ). The resulting feature models can be used for configuration, planning, evolution, reasoning about variants, or keeping an overview understanding of complex software platforms. We systematically engineered the process based on empirically elicited modeling principles. We evaluated and refined it in a real-world industrial case study, two surveys with industrial and academic feature-modeling experts, as well as an open-source case study. We hope that FM-PRO helps to adopt feature models and that it facilitates higher-level, feature-oriented engineering practices, establishing features as a better and more abstract way to manage increasingly complex codebases.

Development and maintenance in variant-rich systems often involves the replication of specific software code, known as software cloning. This process allows for code reuse but presents challenges in managing independently evolving variants. This paper discusses the necessity of effective clone management tools to maintain code quality and efficiency. We present an extension1 to the HAnS IDE plugin. This extension enhances the plugin by supporting basic clone management, and by facilitating the tracking and synchronization of cloned assets and features through a well-designed, lightweight trace database. The plugin is evaluated through unit and integration testing, as well as user experiments, demonstrating its effectiveness in addressing the challenges associated with software cloning. The evaluation results indicate that 80% of participants rated the trace database as intuitive, and 100% rated the notification system as both intuitive and user-friendly.

Customization is a general trend in software engineering, demanding systems that support variable stakeholder requirements. Two opposing strategies are commonly used to create variants: software clone & own and software configuration with an integrated platform. Organizations often start with the former, which is cheap and agile, but does not scale. The latter scales by establishing an integrated platform that shares software assets between variants, but requires high up-front investments or risky migration processes. So, could we have a method that allows an easy transition or even combine the benefits of both strategies? We propose a method and tool that supports a truly incremental development of variant-rich systems, exploiting a spectrum between the opposing strategies. We design, formalize, and prototype a variability-management framework: the virtual platform. Virtual platform bridges clone & own and platform-oriented development. Relying on programming-language independent conceptual structures representing software assets, it offers operators for engineering and evolving a system, comprising: traditional, asset-oriented operators and novel, feature-oriented operators for incrementally adopting concepts of an integrated platform. The operators record meta-data that is exploited by other operators to support the transition. Among others, they eliminate expensive feature-location effort or the need to trace clones. A cost-and-benefit analysis of using the virtual platform to simulate the development of a real-world variant-rich system shows that it leads to benefits in terms of saved effort and time for clone detection and feature location. Furthermore, we present a user study indicating that the virtual platform effectively supports exploratory and hands-on tasks, outperforming manual development concerning correctness. We also observed that participants were significantly faster when performing typical variability management tasks using the virtual platform. Furthermore, participants perceived manual development to be significantly more difficult than using the virtual platform, preferring virtual platform for all our tasks. We supplement our findings with recommendations on when to use virtual platform and on incorporating the virtual platform in practice.

The ever-growing need for customization creates a need to maintain software systems in many different variants. To avoid having to maintain different copies of the same model, developers of modeling languages and tools have recently started to provide implementation techniques for such variant-rich systems, notably variability mechanisms, which support implementing the differences between model variants. Available mechanisms either follow the annotative or the compositional paradigm, each of which have dedicated benefits and drawbacks. Currently, language and tool designers select the used variability mechanism often solely based on intuition. A better empirical understanding of the comprehension of variability mechanisms would help them in improving support for effective modeling. In this article, we present an empirical assessment of annotative and compositional variability mechanisms for three popular types of models. We report and discuss findings from a family of three experiments with 164 participants in total, in which we studied the impact of different variability mechanisms during model comprehension tasks. We experimented with three model types commonly found in modeling languages: class diagrams, state machine diagrams, and activity diagrams. We find that, in two out of three experiments, annotative technique lead to better developer performance. Use of the compositional mechanism correlated with impaired performance. For all three considered tasks, the annotative mechanism was preferred over the compositional one in all experiments. We present actionable recommendations concerning support of flexible, tasks-specific solutions, and the transfer of established best practices from the code domain to models.