SPLC '21: Proceedings of the 25th ACM International Systems and Software Product Line Conference - Volume B

Full Citation in the ACM Digital Library

SESSION: Doctoral symposium

LIFTS: learning featured transition systems

This PhD project aims to automatically learn transition systems capturing the behaviour of a whole family of software-based systems. Reasoning at the family level yields important economies of scale and quality improvements for a broad range of systems such as software product lines, adaptive and configurable systems. Yet, to fully benefit from the above advantages, a model of the system family's behaviour is necessary. Such a model is often prohibitively expensive to create manually due to the number of variants. For large long-lived systems with outdated specifications or for systems that continuously adapt, the modelling cost is even higher. Therefore, this PhD proposes to automate the learning of such models from existing artefacts. To advance research at a fundamental level, our learning target are Featured Transition Systems (FTS), an abstract formalism that can be used to provide a pivot semantics to a range of variability-aware state-based modelling languages. The main research questions addressed by this PhD project are: (1) Can we learn variability-aware models efficiently? (2) Can we learn FTS in a black-box fashion? (i.e., with access to execution logs but not to source code); (3) Can we learn FTS in a white/grey-box testing fashion? (i.e., with access to source code); and (4) How do the proposed techniques scale in practice?

Consistent management of variability in space and time

Development and maintenance of software-intensive systems face major challenges. To cope with an increasing demand for customization, systems need to exist in concurrent variations at a single point in time (i.e., variability in space). Furthermore, as longevity of systems increases, it is necessary to continuously maintain sequential variations due to evolution (i.e., variability in time). Finally, systems are often built from different kinds of artifacts, such as source code or diagrams, that need to be kept consistent. Managing these challenges - the evolution of variable systems composed of heterogeneous artifacts in a consistent and integrated way - is highly demanding for engineers. To tackle the described challenges, we propose an approach for consistent, view-based management of variability in space and time. Therefore, we study, identify, and unify concepts and operations of approaches and tools dealing with variability in space and time to provide a common ground for comparing existing work and encouraging novel solutions. Furthermore, we identify consistency preservation challenges related to view-based evolution of variable systems composed of heterogeneous artifacts, such as the consistent propagation of changes between products, and across the different types of artifacts. We provide a technique for (semi-)automated detection and repair of variability-related inconsistencies. The goal of this doctoral work is to develop an integrated solution for dealing with the described challenges and, thus, advance state of the art towards uniform management of variability in space and time.

STARS: software technology for adaptable and reusable systems

Dynamic Software Product Lines (DSPLs) engineering implements self-adaptive systems by dynamically binding or unbinding features at runtime according to a feature model. However, these features may interact in unexpected and undesired ways leading to critical consequences for the DSPL. Moreover, (re)configurations may negatively affect the runtime system's architectural qualities, manifesting architectural bad smells. These issues are challenging to detect due to the combinatorial explosion of the number of interactions amongst features. As some of them may appear at runtime, we need a runtime approach to their analysis and mitigation. This thesis introduces the Behavioral Map (BM) formalism that captures information from different sources (feature model, code) to automatically detect these issues. We provide behavioral map inference algorithms. Using the Smart Home Environment (SHE) as a case study, we describe how a BM is helpful to identify critical feature interactions and architectural smells. Our preliminary results already show promising progress for both feature interactions and architectural bad smells identification at runtime.

A flexible approach for transforming variability models

In software product lines, engineers use variability models to explicitly represent commonalities and variability. A plethora of variability modeling approaches have been proposed in the last 30 years, and there is no standard variability modeling approach the community agrees on. Well-known approaches such as feature modeling or decision modeling exist in many different variants, most of which have been shown to be useful for at least one specific use case. Due to this variety of approaches researchers and practitioners alike struggle to find, understand, and eventually pick the right approach for a specific context or (set of) system(s). Practitioners in industry often develop custom solutions to manage the variability of various artifacts, like requirements documents or design spreadsheets. In this paper, we report on our ongoing research towards developing a framework for (semi-)automatically transforming variability models. Our approach supports researchers and practitioners experimenting with and comparing different variability modeling approaches and switching from one modeling approach to another. We present the research questions guiding our research and discuss the current status of our work as well as future work.

DEMONSTRATION SESSION: Demonstrations and tools

Static analysis and family-based model checking of featured transition systems with VMC

A Featured Transition System (FTS) is a formalism for modeling variability in configurable system behavior. The behavior of all variants (products) is modeled in a single compact FTS by associating the possibility to perform an action and transition from one state to another with feature expressions that condition the execution of an action in specific variants. We present a front-end for the research tool VMC. The resulting toolchain allows a modeler to analyze an FTS for ambiguities (dead or false optional transitions and hidden deadlock states), transform an ambiguous FTS into an unambiguous one, and perform an efficient kind of family-based verification of an FTS without hidden deadlock states. We use benchmarks from the literature to demonstrate the novelties offered by the toolchain.

HAnS: IDE-based editing support for embedded feature annotations

When developers maintain or evolve software, they often need to know the locations of features. This proves challenging when the feature locations are not documented, when the code was written by different developers who may have left the organization, or when the developer's memory of the implementation has faded. Automated feature location techniques are hard to adopt in practice, especially since they boast too many false positives. To address these challenges, embedded feature annotations have been proposed to allow developers to trace features in code during development with minimal effort. However, tool support is needed for developers to effectively record and use these annotations. We propose HAnS as a tool to meet this need; it is implemented as an IntelliJ IDE plugin to support developers seamlessly record feature locations while they write their code. HAnS supports developers when mapping features to software assets, such as files and code fragments, with code completion and syntax highlighting. It also provides functionality to browse feature definitions and locations, as well as refactor features. A demo video is available at https://youtu.be/cx_-ZshHLgA.

A spaCy-based tool for extracting variability from NL requirements

In previous work, we have shown that ambiguity detection in requirements can also be used as a way to capture latent aspects of variability. Natural Language Processing (NLP) tools have been used for a lexical analysis aimed at ambiguity indicators detection, and we have studied the necessary adaptations to those tools for pointing at potential variability, essentially by adding specific dictionaries for variability. We have identified also some syntactic rules able to detect potential variability, such as disjunction between nouns or pairs of indicators in a subordinate proposition. This paper describes a new prototype NLP tool, based on the spaCy library, specifically designed to detect variability. The prototype is shown to preserve the same recall exhibited by previously used lexical tools, with a higher precision.

BURST: a benchmarking platform for uniform random sampling techniques

We present BURST, a benchmarking platform for uniform random sampling techniques. With BURST, researchers have a flexible, controlled environment in which they can evaluate the scalability and uniformity of their sampling. BURST comes with an extensive --- and extensible --- benchmark dataset comprising 128 feature models, including challenging, real-world models of the Linux kernel. BURST takes as inputs a sampling tool, a set of feature models and a sampling budget. It automatically translates any feature model of the set in DIMACS and invokes the sampling tool to generate the budgeted number of samples. To evaluate the scalability of the sampling tool, BURST measures the time the tool needs to produce the requested sample. To evaluate the uniformity of the produced sample, BURST integrates the state-of-the-art and proven statistical test Barbarik. We envision BURST to become the starting point of a standardisation initiative of sampling tool evaluation. Given the huge interest of research for sampling algorithms and tools, this initiative would have the potential to reach and crosscut multiple research communities including AI, ML, SAT and SPL.

AutoSMP: an evaluation platform for sampling algorithms

Testing configurable systems is a challenging task due to the combinatorial explosion problem. Sampling is a promising approach to reduce the testing effort for product-based systems by finding a small but still representative subset (i.e., a sample) of all configurations for testing. The quality of a generated sample wrt. evaluation criteria such as run time of sample generation, feature coverage, sample size, and sampling stability depends on the subject systems and the sampling algorithm. Choosing the right sampling algorithm for practical applications is challenging because each sampling algorithm fulfills the evaluation criteria to a different degree. Researchers keep developing new sampling algorithms with improved performance or unique properties to satisfy application-specific requirements. Comparing sampling algorithms is therefore a necessary task for researchers. However, this task needs a lot of effort because of missing accessibility of existing algorithm implementations and benchmarks. Our platform AutoSMP eases practitioners and researchers lifes by automatically executing sampling algorithms on predefined benchmarks and evaluating the sampling results wrt. specific user requirements. In this paper, we introduce the open-source application of AutoSMP and a set of predefined benchmarks as well as a set of T-wise sampling algorithms as examples.

WORKSHOP SESSION: VM4ModernTech 2021: International workshop on variability management for modern technologies

Automated derivation of variants in manufacturing systems design

The Logistics Specification and Analysis Tool (LSAT) is a modelbased engineering tool used for design-space exploration of flexible manufacturing systems. LSAT provides domain specific languages to model a manufacturing system and means to analyze the productivity characteristics of such a system. In LSAT, developers can specify a system and model its deterministic operations as a set of activities. Given a set of activities, it is possible to construct an individual activity sequence that represents one valid system execution, and with minor variations in the specification individual systems can be obtained. To avoid modeling each variant separately, which means cloning and maintaining the common parts, new functionality is needed to deal with the variability of system specifications. In this study, we aim to establish integration between LSAT and product line engineering techniques. Specifically, we provide a realization of a toolchain including variability representation of LSAT realization artifacts and automated variant derivation for the LSAT model variants. Delta modeling, a transformational variability realization mechanism, is employed to model the variability within LSAT realization artifacts. Using the toolchain, we develop an industry-related case for a product line, the so called Extended Twilight System, a Cyber Physical System (CPS) inspired by the CPSs of our industrial partner.

Transfer learning for multiobjective optimization algorithms supporting dynamic software product lines

Dynamic Software Product Lines (DSPLs) are a well-accepted approach for self-adapting Cyber-Physical Systems (CPSs) at run-time. The DSPL approaches make decisions supported by performance models, which capture system features' contribution to one or more optimization goals. Combining performance models with Multi-Objectives Evolutionary Algorithms (MOEAs) as decision-making mechanisms is common in DSPLs. However, MOEAs algorithms start solving the optimization problem from a randomly selected population, not finding good configurations fast enough after a context change, requiring too many resources so scarce in CPSs. Also, the DSPL engineer must deal with the hardware and software particularities of the target platform in each CPS deployment. And although each system instantiation has to solve a similar optimization problem of the DSPL, it does not take advantage of experiences gained in similar CPS. Transfer learning aims at improving the efficiency of systems by sharing the previously acquired knowledge and applying it to similar systems. In this work, we analyze the benefits of transfer learning in the context of DSPL and MOEAs testing on 8 feature models with synthetic performance models. Results are good enough, showing that transfer learning solutions dominate up to 71% of the non-transfer learning ones for similar DSPL.

Product-lining the elinvar wealthtech microservice platform

Software product lining is the act of providing different but related software products under the same brand, known as a software product line (SPL). As engineering, management and validation of SPLs is far from trivial, special solutions for software product line engineering (SPLE) have a continuous momentum in both academic and industry. In general, it is hard to judge when to reasonably favor SPLE over alternative solutions that are more common in the industry. In this paper, we illustrate how we as Elinvar manage variability within our WealthTech Platform as a Service (PaaS) at different granularity levels, and discuss methods for SPLE in this context. More in detail, we share our techniques and concepts to address configuration management, and show how we manage a single microservice SPL including inter-service communication. Finally, we provide insights into platform solutions by means of packages for our clients. We end with a discussion on SPLE techniques in context of service SPLs and our packaging strategy. We conclude that while we are good to go with industry-standard approaches for microservice SPLs, the variability modeling and analysis advantages within SPLE is promising for our packaging strategy.

WORKSHOP SESSION: MODEVAR@SPLC 2021: 4th international workshop on languages for modelling variability

How flexible must a transformation approach for variability models and custom variability representations be?

A plethora of variability modeling approaches has been developed in the last 30 years. Feature modeling approaches are probably the most common and well-known approaches. All existing variability modeling approaches have their benefits and drawbacks and have been shown to be useful at least in certain use cases. Nevertheless, industry frequently develops their own custom solutions to manage variability because they struggle picking an approach from the (still growing) number of modeling approaches available. Therefore, we work towards a transformation approach, which enables researchers and practitioners alike to compare different (custom) variability modeling approaches and representations and switch in between them at least (semi-)automatically. In this paper, we discuss ongoing challenges for the transformation approach regarding the implementation of the transformations and the expected flexibility of the approach. We present our research agenda towards a flexible and adaptable transformation approach for well-known variability modeling approaches and custom variability representations used in industry.

Integration of UVL in FeatureIDE

Variability models are prevalent for specifying the commonalities and variabilities of configurable systems. A large variety of tools support using, editing, and analyzing variability models. However, the different tools often depend on distinct textual notations to store and read variability models which induces a large effort for researchers and practitioners. This additional effort could be reduced if the community adopted a single format. Following the goal of the MODEVAR initiative to develop a widely adopted variability language, we provided a first proposal with the Universal Variability language (UVL) in previous work. For a textual format to be adopted, an important aspect is an as small as possible effort when integrating the format in other tools. In this work, we discuss the integration of UVL in FeatureIDE. We use the integration to examine the applicability of UVL and our parser library to existing tools and gather further requirements for the language design. Furthermore, we provide a thorough documentation on the implementation to be used as reference and guidance for integration in other tools.

A first prototype of a new repository for feature model exchange and knowledge sharing

Feature models are the "de facto" standard for variability modelling and are used in both academia and industry. The MODEVAR initiative tries to establish a common textual feature modelling language that can be used by different communities and can allow information sharing. Feature model related researches use different models for different purposes such as analysis, sampling, testing, debugging, teaching, etc. Those models are shared in private repositories and there is a risk that all that knowledge is spread across different platforms which hinder collaboration and knowledge reuse. In this paper, we propose a first working version of a new feature model repository that allows to centralise the knowledge generated in the community together with advanced capabilities such as DOI generation, an API, analysis reports, among others. Our solution is a front end interface that uses the popular open science repository Zenodo as an end point to materialise the storage of all the information. Zenodo is enhanced with characteristics that facilitate the management of the models. The idea of our repository is to provide existing but also new features that are not present in other repositories (e.g., SPLOT). We propose to populate our repository with all the existing models of many sources including SPLOT.

Optimisation for the product configuration system of Renault: towards an integration of symmetries

The problem of configuring model variability is widespread in many different domains. Renault, a leading french automobile manufacturer, has developed its technology internally to model vehicle diversity. This technology relies on the approach known as knowledge compilation. Since its inception, continuous progress has been made in the tool while monitoring the latest developments from the software field and academia. However, the growing number of vehicle models brings potential risks and higher requirements for the tool. This paper presents a short reminder of Renault's technology principles and the improvements we intend to achieve by analyzing and leveraging notable data features of Renault problem instances. In particular, the aim is to exploit symmetry properties.

WORKSHOP SESSION: REVE 2021: 9th international workshop on reverse variability engineering

Extending the identification of object-oriented variability implementations using usage relationships

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.

Product-line analysis cookbook: a classification system for complex analysis toolchains

Adopting Product Line Engineering (PLE) approaches in the context of software-intensive systems reduces overall development and maintenance costs, reduces time to market and leads to an overall improvement in product quality. The Software and System Product Line (SPL) community has provided a large number of different analysis approaches and tools, which were developed in different contexts, answer different questions, and can contribute to the fulfillment of different analysis goals. Typically, these analysis tools are initially developed as part of a research study, where they serve a specific purpose, e. g. for investigating the use of a new technology, or to demonstrate the transfer of methods from other fields. Generally, such purpose is aligned with a specific, but not explicitly stated, high-level goal. The pursuit of these goals requires holistic approaches, i. e. integrated toolchains and classification of analyses, which are documented as a centralized collection of wisdom. Therefore, we propose a classification system which describes existing analyses and reveals possible combinations, i. e. integrated toolchains, and provide first examples. This method supports the search for toolchains which address complex industrial needs. With the support of the SPL community, we hope to collaboratively document existing analyses and corresponding goals on an open platform.

WORKSHOP SESSION: WEESR2021: 4th workshop on experiences and empirical studies on software reuse

A reusable set of real-world product line case studies for comparing variability models in research and practice

Real-world cases describing (product) variability in production systems are rare and often not accessible. Thus, researchers often use toy examples or develop fictitious case studies. These are designed to demonstrate their approach but rarely to compare multiple approaches. In this paper, we aim at making variability modeling evaluations comparable. We present and provide a reusable set of four real-world case studies that are easy to access, with artifacts represented in a universal, variability-model-agnostic way, the industrial Product-Process-Resource Domain-Specific Language (PPR DSL). We report how researchers can use the case studies, automatically transforming the Domain-Specific Language (DSL) artifacts to well-known variability models, e.g., product feature models, using the Variability Evolution Roundtrip Transformation (VERT) process. We compare the expressiveness and complexity of the transformed feature models. We argue that the case studies with the DSL and the flexible transformation capabilities build a valuable contribution to making future research results more comparable and facilitating evaluations with real-world product lines.

WORKSHOP SESSION: VariVolution 2021: 4th international workshop on variability and evolution of software-intensive systems

Iterative development and changing requirements: drivers of variability in an industrial system for veterinary anesthesia

Developing a safety-critical embedded system poses a high risk, since such systems must usually comply with (potentially changing) rigorous standards set by customers and legal authorities. To reduce risk and cope with changing requirements, manufacturers of embedded devices increasingly use iterative development processes and prototyping both for hard- and firmware. However, hard- and firmware development are difficult to align in a common process, because hardware development cycles are typically longer and more expensive. Thus, seamlessly transitioning software to new hardware revisions and reusing old hardware revisions can be problematic. In this paper, we describe an industrial case study for veterinary anesthesia in which we also faced this problem. To solve it, we introduced preprocessor-based variability to create a small configurable system that could flexibly adapt to our needs. We discuss our solution, alternative solutions for hardware evolution, as well as their pros and cons. Our experiences generalize an interesting evolution scenario for systems that are planned and delivered as a single system, but exhibited variability to cope with problems during agile development processes.

Towards heterogeneous multi-dimensional variability modeling in cyber-physical production systems

Cyber-Physical Production Systems (CPPSs) are complex systems interacting with their environment by sensors and actuators. Such systems typically have a long lifespan, over which a plethora of variants are developed and maintained. The heterogeneity of hardware and software components used in CPPSs and the multiple disciplines (mechanical, electrical, software engineering) involved in the development and maintenance of CPPSs, however, make it difficult to manage their variability. Specifically, variability needs to be expressed in and across multiple disciplines, which use heterogeneous methods and tools. This also affects configuration as well as co-evolution of models and artifacts. In this short paper, we discuss our first ideas towards a Heterogeneous Multi-Dimensional Variability Modeling approach for CPPSs. Our approach builds on and extends existing work to address the challenges of modeling the variability of CPPSs and supporting their configuration and evolution. We showcase our idea using a case study system and outline a research agenda.