An Exploratory Study on Applying a Scrum Development Process for Safety-Critical Systems

Abstract

Abstract. Background: Agile techniques recently have received attention from the developers of safety-critical systems. However, a lack of empirical knowledge of performing safety assurance techniques, especially safety analysis in a real agile project hampers further steps. Aims: In this article, we aim at (1) understanding and optimizing the S-Scrum development process, a Scrum extension with the integration of a systems theory based safety analysis technique, STPA (System-Theoretic Process Analysis), for safety-critical systems; (2) validating the Optimized S-Scrum development process further. Method: We conducted a two-stage exploratory case study in a student project at the University of Stuttgart, Germany. Results: The results in stage 1 showed that S-Scrum helps to ensure safety of each release but is less agile than the normal Scrum. We explored six challenges on: priority management; communication; time pressure on determining safety requirements; safety planning; time to perform upfront planning; and safety requirements' acceptance criteria. During stage 2, the safety and agility have been improved after the optimizations, including an internal and an external safety expert; pre-planning meeting; regular safety meeting; an agile safety plan; and improved safety epics and safety stories. We have also gained valuable suggestions from industry, but the generalization problem due to the specific context is still unsolved.

Meshing agile and plan-driven development in safety-critical software: a case study

“…Managing iterative changes (Beznosov 2003;Beznosov and Kruchten 2004;Jonsson et al 2012;Notander et al 2013a; Van Schooenderwoert and Shoemaker 2018) 2. Iterative validation of the software (Kasauli et al 2018;Paige et al 2008;Wang et al 2017;Wang and Wagner 2018) • Conduct the safety analysis iteratively, but validate the software incrementally (Kasauli et al 2018 (Jonsson et al 2012) 3. Heavy iterative testing of the software increments (Kasauli et al 2018;Rottier and Rodrigues 2008) • Use longer iterations to include testing and validation (Rasmussen et al 2009;Rottier and Rodrigues 2008) • Use automated, risk-based, continuous testing (Kasauli et al 2018)…”

“…Notander et al (2013a) and Van Schooenderwoert and Shoemaker (2018) suggested an iterative framework for safety-critical software development in which documentation is also treated iteratively and incrementally. Wang et al (2017) and Wang and Wagner (2018) stated how traditional safety analysis and verification techniques are difficult to use with agile software development. Wang et al (2017) proposed a process called S-Scrum, which uses a hazard analysis technique called System-Theoretic Process Analysis (STPA) and allows for an iterative validation, and Wang and Wagner (2018) proposed using a combination of STPA and Behavior-Driven Development (BDD).…”

Safety-Critical Systems and Agile Development: A Mapping Study

“…Create software development plan [KKK14] based on features [RHJS09] at the planning meeting [SHMH14], [HHS + 16]. Document chosen modelling approach, implementation language, development environment and assessment tools [DK16] and determine safety requirements [WRW17]. Combine sprint planning with retrospective [SM16b], [RHJS09], [McM16] to empirically improve estimations [FSOO13].…”

Combining STPA and BDD for Safety Analysis and Verification in Agile Development: A Controlled Experiment

“…In 2016, we proposed to use STPA in a Scrum development process [5]. It showed a good capability to ensure agility and safety in a student project [12]. However, we verified the safety requirements only at the end of each sprint by executing UAT together with TDD in development.…”

“…Thus, a BDD test scenario should test if the ultrasonic sensor provides the feedback that the forward distance <= threshold (means there is an 2 Since we focus on safety in our research, we assign a safety analyst as the QA role in our context. 3 More descriptions of STPA for safety analysis are given in [7] concerning an example of using STPA in an airbag system and [12] concerning the use of STPA in a Scrum development process. 4 We illustrate a BDD test scenario using only three basic steps "Given" "When" "Then".…”