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Aspects of complexity in automotive software systems and their relation to maintainability effort. A case study

Bengt Haraldsson, Miroslaw Staron

TL;DR

The paper examines how maintainability effort in automotive embedded software relates to multiple sources of complexity, including code, product variants, and organizational factors. Using a mixed-method case study at Scania with two large systems, it links quantitative metrics (cyclomatic complexity, fan-in/fan-out, LOC) to qualitative developer perceptions gathered through interviews, showing that variant management, legacy code, and hardware-control tasks drive maintainability effort alongside external coordination and regulatory considerations. The study demonstrates alignment between code/variant metrics and perceived complexity, and identifies trade-off strategies developers use to minimize effort while maintaining risk, suggesting that a holistic metric set that captures external complexity is needed for accurate maintainability assessment. Practically, the findings inform how teams can structure organizations and build processes to manage complexity more effectively in long-lived automotive software ecosystems.

Abstract

Context: Large embedded systems in vehicles tend to grow in size and complexity, which causes challenges when maintaining these systems. Objective: We explore how developers perceive the relation between maintainability effort and various sources of complexity. Methods: We conduct a case study at Scania AB, a heavy vehicle OEM. The units of analysis are two large software systems and their development teams/organizations. Results: Our results show that maintainability effort is driven by system internal complexity in the form of variant management and complex hardware control tasks. The maintainability is also influenced by emergent complexity caused by the system's longevity and constant growth. Besides these system-internal complexities, maintainability effort is also influenced by external complexities, such as organizational coordination and business needs. During the study, developer trade-off strategies for minimizing maintainability effort emerged. Conclusions: Complexity is a good proxy of maintainability effort, and allows developers to create strategies for managing the maintainability effort. Adequate complexity metrics include both external aspects -- e.g., coordination complexity -- and internal ones -- e.g., McCabe Cyclomatic Complexity.

Aspects of complexity in automotive software systems and their relation to maintainability effort. A case study

TL;DR

The paper examines how maintainability effort in automotive embedded software relates to multiple sources of complexity, including code, product variants, and organizational factors. Using a mixed-method case study at Scania with two large systems, it links quantitative metrics (cyclomatic complexity, fan-in/fan-out, LOC) to qualitative developer perceptions gathered through interviews, showing that variant management, legacy code, and hardware-control tasks drive maintainability effort alongside external coordination and regulatory considerations. The study demonstrates alignment between code/variant metrics and perceived complexity, and identifies trade-off strategies developers use to minimize effort while maintaining risk, suggesting that a holistic metric set that captures external complexity is needed for accurate maintainability assessment. Practically, the findings inform how teams can structure organizations and build processes to manage complexity more effectively in long-lived automotive software ecosystems.

Abstract

Context: Large embedded systems in vehicles tend to grow in size and complexity, which causes challenges when maintaining these systems. Objective: We explore how developers perceive the relation between maintainability effort and various sources of complexity. Methods: We conduct a case study at Scania AB, a heavy vehicle OEM. The units of analysis are two large software systems and their development teams/organizations. Results: Our results show that maintainability effort is driven by system internal complexity in the form of variant management and complex hardware control tasks. The maintainability is also influenced by emergent complexity caused by the system's longevity and constant growth. Besides these system-internal complexities, maintainability effort is also influenced by external complexities, such as organizational coordination and business needs. During the study, developer trade-off strategies for minimizing maintainability effort emerged. Conclusions: Complexity is a good proxy of maintainability effort, and allows developers to create strategies for managing the maintainability effort. Adequate complexity metrics include both external aspects -- e.g., coordination complexity -- and internal ones -- e.g., McCabe Cyclomatic Complexity.
Paper Structure (29 sections, 4 figures, 4 tables)

This paper contains 29 sections, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Theoretical Framework
  3. Related Work
  4. Methodology
  5. Case Description
  6. Quantitative Metrics Analysis for Maintainability (RQ2, RQ3)
  7. Developer Perception Analysis (RQ1, RQ2, RQ3)
  8. Results
  9. Code metric analysis
  10. Products A:1 and A:2
  11. Product B:1 and B:2
  12. Variant and structure analysis
  13. Thematic analysis
  14. Higher number of variants lead to higher complexity and maintainability effort
  15. Difficulty describing functional requirements impacts testing
  16. ...and 14 more sections

Figures (4)

  • Figure 1: Theoretical Framework
  • Figure 2: Complexity metrics for A:1 and A:2. The diagrams show that the distributions are similar between these two versions, but A:2 is larger in size in terms of a number of functions.
  • Figure 3: Complexity metrics for B:1 and B:2. The diagrams show that the distributions are similar between these two versions, indicating that external deliveries do not influence product complexity to any greater extent.
  • Figure 4: Expanded theoretical framework. Additions highlighted with pink lines.