Long-Term Average Cost in Featured Transition Systems

A software product line is a family of software products that share a common set of mandatory features and whose individual products are differentiated by their variable (optional or alternative) features. Family-based analysis of software product lines takes as input a single model of a complete product line and analyzes all its products at the same time. As the number of products in a software product line may be large, this is generally preferable to analyzing each product on its own. Family-based analysis, however, requires that standard algorithms be adapted to accomodate variability. In this paper we adapt the standard algorithm for computing limit average cost of a weighted transition system to software product lines. Limit average is a useful and popular measure for the long-term average behavior of a quality attribute such as performance or energy consumption, but has hitherto not been available for family-based analysis of software product lines. Our algorithm operates on weighted featured transition systems, at a symbolic level, and computes limit average cost for all products in a software product line at the same time. We have implemented the algorithm and evaluated it on several examples

Towards Sampling and Simulation-Based Analysis of Featured Weighted Automata

International audienceWe consider the problem of model checking Variability-Intensive Systems (VIS) against non-functional requirements. These requirements are typically expressed as an optimization problem over quality attributes of interest, whose value is determined by the executions of the system. Identifying the optimal variant can be hard for two reasons. First, the state-explosion problem inherent to model checking makes it increasingly complex to find the optimal executions within a given variant. Second, the number of variants can grow exponentially with respect to the number of variation points in the VIS. In this paper, we lay the foundations for the application of smart sampling and statistical model checking to solve this problem faster. We design a simple method that samples variants and executions in a uniform manner from a featured weighted automaton and that assesses which of the sampled variants/executions are optimal. We implemented our approach on top of ProVeLines, a tool suite for model-checking VIS and carried out a preliminary evaluation on an industrial embedded system design case study. Our results tend to show that sampling-based approaches indeed holds the potential to improve scalability but should be supported by better sampling heuristics to be competitive

Quantitative Analyses of Software Product Lines

A software product-line (SPL) is a family of related software systems that are jointly developed and reuse a set of shared assets. Each individual software system in an SPL is called a software product and includes a set of mandatory and optional features, which are independent units of functionality. Software-analysis techniques, such as model checking, analyze a model of a software system to determine whether the software system satisfies its requirements. Because many software-analysis techniques are computationally intensive, and the number of software products in an SPL grows exponentially with the number of features in an SPL, it tends to be very time consuming to individually analyze each product of an SPL. Family-based analyses have adapted standard software-analysis techniques (e.g., model checking, type checking) to simultaneously analyze all of the software products in an SPL, reusing partial analysis results between different software products to speed up the analysis. However, these family-based analyses verify only the functional requirements of an SPL, and we are interested in analyzing the quality of service that different software products in an SPL would exhibit. Quantitative analyses of a software system model (e.g., of a weighted transition system) can estimate how long a system will take to reach its goal, how much energy a system will consume, and so on. Quantitative analyses are known to be computationally intensive. In this thesis, we investigate whether executing a family-based quantitative analysis on a model of an SPL is faster than individually analyzing every software product of the SPL. First, we present a family-based trace-checking analysis that facilitates the reconfig- uration of a dynamic software product line (DSPL), which is a type of SPL in which features can be activated or deactivated at runtime. We assessed whether executing the family-based trace-checking analysis is faster than executing the trace-checking analysis on every software product in three case studies. Our results indicated that the family-based trace checking analysis, when combined with simple data-abstraction over an SPL model’s quality-attribute values to facilitate sharing of partial-analysis results, is between 1.4 and 7.7 times faster than individually analyzing each software product. This suggests that abstraction over the quality-attribute values is key to make family-based trace-checking analysis efficient. Second, we consider an SPL’s maximum long-term average value of a quality attribute (e.g., because it represents the long-term rate of energy consumption of the system). Specifically, the maximum limit-average cost of a weighted transition represents an upper bound on the long-term average value of a quality attribute over an infinite execution of the system. Because computing the maximum limit-average cost of a software system is computationally intensive, we developed a family-based analysis that simultaneously computes the maximum limit-average cost for each software product in an SPL. We assessed its per- formance compared to individually analyzing each software product in two case studies. Our results suggest that our family-based analysis will perform best in SPLs in which many products share the same set of strongly connected components. Finally, because both of our family-based analyses require as input a timed (weighted) behaviour model of a Software Product Line, we present a method to learn such a timed (weighted) behaviour model. Specifically, the objective is to learn, for each transition t, a regression function that maps a software product to a real-valued weight that represents the duration of transition t’s execution in that software product. We apply supervised learning techniques, linear regression and regularized linear regression, to learn such functions. We assessed the accuracy of the learnt models against ground truth in two different SPL and also compared the accuracy of our method against two different state-of-the-art methods: Perfume and a Performance-Influence model. Our results indicate that the accuracy of our learnt models ranged from a mean error of 3.8% to a mean error of 193.0%. Our learnt models were most accurate for those transitions whose execution times had low variance across repeated executions of the transition in the same software product, and in which there is a linear relationship between the transition’s execution time and the presence of features in a software product