Abstract
ContextModels, as the main artifact in model-driven engineering, have been extensively used in the area of embedded systems for code generation and verification. One of the most popular behavioral modeling techniques is the state machine. Many state machine modeling guidelines recommend that a state machine should have more than one state in order to be meaningful. However, single-state state machines (SSSMs) violating this recommendation have been used in modeling cases reported in the literature.ObjectiveWe aim for understanding the phenomenon of using SSSMs in practice as understanding why developers violate the modeling guidelines is the first step towards improvement of modeling tools and practice.MethodTo study the phenomenon, we conducted an exploratory study which consists of two complementary studies. The first study investigated the prevalence and role of SSSMs in the domain of embedded systems, as well as the reasons why developers use them and their perceived advantages and disadvantages. We employed the sequential explanatory strategy, including repository mining and interview, to study 1500 state machines from 26 components at ASML, a leading company in manufacturing lithography machines from the semiconductor industry. In the second study, we investigated the evolutionary aspects of SSSMs, exploring when SSSMs are introduced to the systems and how developers modify them by mining the largest state-machine-based component from the company.ResultsWe observe that 25 out of 26 components contain SSSMs. Our interviews suggest that SSSMs are used to interface with the existing code, to deal with tool limitations, to facilitate maintenance and to ease verification. Our study on the evolutionary aspects of SSSMs reveals that the need for SSSMs to deal with tool limitations grew continuously over the years. Moreover, only a minority of SSSMs have been changed between SSSM and multiple-state state machine (MSSM) during their evolution. The most frequent modifications developers made to SSSMs is inserting events with constraints on the execution of the events.ConclusionsBased on our results, we provide implications for developers and tool builders. Furthermore, we formulate hypotheses about the effectiveness of SSSMs, the impacts of SSSMs on development, maintenance and verification as well as the evolution of SSSMs.
Highlights
Models play a central role in model-driven engineering (MDE) (Whittle et al 2014)
Communicated by: Georgios Gousios and Sarah Nadi This article belongs to the Topical Collection: Mining Software Repositories (MSR)
We construct a 2 × 2 contingency table recording the number of Single-state state machines (SSSMs)-Interface Models (IM) and multiple-state state machine (MSSM)-IMs for each location
Summary
Models play a central role in model-driven engineering (MDE) (Whittle et al 2014). While models are typically used to facilitate team communication and serve as implementation blueprints, in the area of embedded systems modeling, models have been extensively used for such goals as code generation, simulation, timing analysis and verification (Liebel et al 2014). Many guidelines have been proposed on how one should model system behavior using state machines (Ambler 2005; Dennis et al 2009; Prochnow 2008; Schaefer 2006). One of the recommendations commonly repeated both in books (Ambler 2005; de San Pedro and Cortadella 2016; Dennis et al 2009) and online resources, is that a state machine model is only meaningful if it contains more than one state, and if each state represents different behavior. The intuition behind this guideline is that a model should contain non-trivial information, otherwise it merely clutters the presentation of ideas (Ambler 2005). From the growing body of software engineering literature we know that software developers do not always follow recommendations or best practices and often have valid reasons not to do so (Businge et al 2013; Palomba et al 2018; Tufano et al 2017)
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