In many variability-intensive systems, variability is implemented in code units provided by a host language, such as classes or functions, which do not align well with the domain features. Annotating or creating an orthogonal decomposition of code in terms of features implies extra effort, as well as massive and cumbersome refactoring activities. In this paper, we introduce an approach for identifying and visualizing the variability implementation places within the main decomposition structure of object-oriented code assets in a single variability-rich system. First, we propose to use symmetry, as a common property of some main implementation techniques, such as inheritance or overloading, to identify uniformly these places. We study symmetry in different constructs (e.g., classes), techniques (e.g., subtyping, overloading) and design patterns (e.g., strategy, factory), and we also show how we can use such symmetries to find variation points with variants. We then report on the implementation and application of a toolchain, symfinder, which automatically identifies and visualizes places with symmetry. The publicly available application to several large open-source systems shows that symfinder can help in characterizing code bases that are variability-rich or not, as well as in discerning zones of interest w.r.t. variability. CCS CONCEPTS• Software and its engineering → Software product lines; Object oriented development; Reusability. KEYWORDSIdentifying software variability, visualizing software variability, object-oriented variability-rich systems, tool support for understanding software variability, software product line engineering

In Software Product Line (SPL) engineering, mapping domain features to existing code assets is essential for variability management. When variability is already implemented through Object-Oriented (OO) techniques, it is too costly and error-prone to refactor assets in terms of features or to use feature annotations. In this work, we delve into the possible usage of automatically identified variation points with variants in an OO code base to enable feature mapping from the domain level. We report on an experiment conducted over ArgoUML-SPL, using its code as input for automatic detection through the symfinder toolchain, and the previously devised domain features as a ground truth. We analyse the relevance of the identified variation points with variants w.r.t. domain features, adapting precision and recall measures. This shows that the approach is feasible, that an automatic mapping can be envisaged, and also that the symfinder visualization is adapted to this process with some slight additions. CCS CONCEPTS • Software and its engineering → Software product lines.

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Most modern object-oriented software systems are variability-rich, despite that they may not be developed as product lines. Their variability is implemented by several traditional techniques in combination, such as inheritance, overloading, or design patterns. As domain features or variation points with variants are not a by-product of these techniques, variability in code assets of such systems is implicit, and hardly documented, hampering qualities such as understandability and maintainability. In this article, we present an approach for automatic identification and visualization of variability implementation places, that is, variation points with variants, in variability-rich systems. To uniformly identify them, we propose to rely on the existing symmetries in the different software constructs and patterns. We then propose to visualize them according to their density. By means of our realized toolchain implementing the approach, symfinder , we report on a threefold evaluation, (i) on the identified potential variability in sixteen large open-source systems and symfinder 's scalability, (ii) on measuring symfinder 's precision and robustness when mapping identified variability to domain features, and (iii) on its usage by a software architect. Results show that symfinder can indeed help in identifying and comprehending the variability of the targeted systems.

Variability is present in most modern object-oriented softwareintensive systems, despite that they commonly do not follow a product line approach. In these systems, variability is implicit and hardly documented as it is implemented by different traditional mechanisms, namely inheritance, overloading, or design patterns. This hampers variability management as automatic identification of variation points (vp-s) with variants is very difficult. symfinder is a symmetry-based tooled approach that enables automatic identification of potential vp-s with variants in such systems. Then, it visualizes them relying on their density in code assets. From the Java-only version presented at SPLC'2019, we present here several notable improvements. They concern an added support for C ++ systems, the identification of vp-s implemented by Decorator and Template pattern instances, an enhanced visualization (e.g., to display all variants, and package coloring), as well as automation of the mapping of potential vp-s to domain features. CCS CONCEPTS • Software and its engineering → Software product lines; Object oriented development; Reusability.

Many variability-rich object-oriented systems rely on multiple traditional techniques (inheritance, patterns) to implement their variability in a single codebase. These variability implementation places are neither explicit nor documented, hampering their detection and variability comprehension. Based on the identification of symmetry property in seven implementation techniques, a first approach was proposed with symfinder to automatically identify and display the variability of a system in a graph-based visualization structured by inheritance. However, composition, or more generally the usage relationship, is extensively used to implement the variability in object-oriented systems, and without this information, comprehending the large amount of variability identified by symfinder is not trivial. In this paper, we present symfinder-2, an extension of the former approach that incorporates the usage relationships to better identify potential variability implementations. We provide two ways to mark classes as entry points, user-defined and automatic, so that the visualization is filtered and enables users to have a better focus when they identify variability. We also report on the evaluation of this extension to ten open-source Java-based systems. CCS CONCEPTS• Software and its engineering → Software product lines; Software reverse engineering; Object oriented architectures.

Many large-scale software systems intensively implement variability to reuse software and speed up development. Such mechanisms, however, bring additional complexity, which eventually leads to technical debt, threatening the software quality, and hampering maintenance and evolution. This is especially the case for variability-rich object-oriented (OO) systems that implement variability in a single codebase. They heavily rely on existing OO mechanisms to implement their variability, making them especially prone to variability debt at the code level. In this paper, we propose Vari-Metrics, an extension of a visualization relying on the city metaphor to reveal such zones of indebted OO variability implementations. VariMetrics extends the VariCity visualization and displays standard OO quality metrics, such as code duplication, code complexity, or test coverage, as additional visual properties on the buildings representing classes. Extended configuration options allow the user to choose and combine quality metrics, uncovering the critical zones of OO variability implementations. We evaluate VariMetrics both by reporting on the exposed quality-critical zones found on multiple large open-source projects, and by correcting the reported issues in such zones of one project, showing an improvement in quality. CCS CONCEPTS• Software and its engineering → Software product lines; Software reverse engineering; Object oriented architectures; • Human-centered computing → Visualization systems and tools.

Many large software systems are variability-rich, object-oriented, and implemented in a single code base. They then rely on multiple traditional techniques (inheritance, patterns) to realize variability, making these implementations not explicit. This directly hampers the comprehension of variability implementations, especially for newcomers in a project that need, in a short time, to understand the most important parts. In this paper, we propose VariCity, a visualization using the city metaphor to exhibit zones of interest, being zones of high density of variability implementations. The different forms of variability implementations are first detected through the usage of symmetries in code (e.g., inheritance defines a substitution symmetry between the immutable part of the superclass and the possible changes in its subclasses). VariCity then creates a 3D city representation with buildings being classes while the metrics on the number of symmetries (e.g., the number of overloaded methods, influence the building size, and their color if they are heavily loaded in symmetries). Contrary to the usual packagebased organization in code-related city representations, the city streets are arranged according to the usage relationships between classes. Inheritance is simply represented with hoverable aerial links. Variability-related design patterns are depicted as buildings with specific geometric forms, while some classes specified as entry points can help in shaping the whole city organization. We also report on the evaluation of VariCity on a set of large objectoriented systems, showing that several usage scenarios helping a newcomer to spot critical variability-related zones are covered.