Requirements Analysis of Variability Constraints in a Configurable Flight Software System

TL;DR

This paper presents a new variability modeling approach for flight software that centralizes requirements, helping to identify inconsistencies and reduce errors in configurable systems used in space missions.

Contribution

The paper introduces a structured variability model for flight software, demonstrating its development, application, and benefits in improving requirement analysis and consistency.

Findings

Helped identify missing variability requirements

Detected inconsistent constraints in the software

Streamlined requirements analysis process

Abstract

Variability constraints are an integral part of the requirements for a configurable system. The constraints specified in the requirements on the legal combinations of options define the space of potential valid configurations for the system-to-be. This paper reports on our experience with the variability-related requirements constraints of a flight software framework used by multiple space missions. A challenge that we saw for practitioners using the current framework, now open-sourced, is that the specifications of its variability-related requirements and constraints are dispersed across several documents, rather than being centralized in the software requirements specification. Such dispersion can contribute to misunderstandings of the side-effects of design choices, increased effort for developers, and bugs during operations. Based on our experience, we propose a new software variability model, similar to a product-line feature model, in the flight software framework. We describe the structured technique by which our model is developed, demonstrate its use, and evaluate it on a key service module of the flight software. Results show that our lightweight modeling technique helped find missing and inconsistent variability-related requirements and constraints. More generally, we suggest that a variability modeling technique such as this can be an efficient way for developers to centralize the specification and improve the analysis of dispersed variability-related requirements and constraints in other configurable systems.