# Requirements-Decision Modeling for Cyber-Physical Systems of Systems

**In short:** ReDeMo is a formal model that links non-functional requirements (qualities such as sustainability) to architectural decisions for cyber-physical systems. It comes from the TaSSAreCt research project and is built into a SysML v2-based toolchain for architects.

## Explanation

Cyber-physical systems (CPS) combine software with physical devices. A cyber-physical system of systems (CPSoS) joins several such systems. The research project TaSSAreCt studies how software architecture can support the sustainability, quality, and long-term evolution of these systems. The Swiss National Science Foundation funds it, and it runs from 2025 to 2028.

One project goal is to find out how CPS influence traditional non-functional properties and new ones. Non-functional requirements (NFRs) describe qualities a system must have, such as speed or reliability. See the articles Quality Attribute and Architectural Decision for background.

ReDeMo is a formal model that links NFRs with architectural decisions. A formal model states these links in a precise, structured way.

The project also builds a knowledge base of architectural decisions and requirements in CPS. The model is implemented in a toolchain based on SysML v2, a modeling language, to support architects.

Sustainability is a key NFR category in this work. It matters most for resource-constrained CPS, which have limited resources to work with.

The University of St. Gallen (HSG) leads the project. ZHAW is listed as a partner.

## Example

A team builds a network of battery-powered field sensors. One requirement says the sensors must run for years without a battery change. Another says they must report readings quickly. With a requirements-to-decisions model, the team records both requirements. It then links each decision, such as how often a sensor transmits, to the requirements it affects. Later, anyone who questions a decision can see which requirements it serves.

## Trade-offs

The available facts do not describe the model's costs or limits. The project runs until 2028, so the model and toolchain are research work in progress. Treat them as an approach to watch, not a settled standard.

Requirements linked to decisions, supported by a knowledge base and a toolchain.

```mermaid
flowchart LR
  R[Non-functional requirements] -->|linked by ReDeMo| D[Architectural decisions]
  K[Knowledge base] --> D
  T[SysML v2 toolchain] --> D
```

## Checks

- Non-functional requirements are explicitly linked to the architectural decisions that address them.
- Sustainability is considered as a requirement category for resource-constrained cyber-physical systems.
- Architectural decisions and requirements are collected in a shared knowledge base.

## Related

- [Architectural Decision](https://arc.fuet.ch/concepts/forces-decisions/architectural-decision.md)
- [Quality Attribute](https://arc.fuet.ch/concepts/quality-attributes/quality-attribute.md)
- [Architecturally Significant Requirement](https://arc.fuet.ch/concepts/forces-decisions/architecturally-significant-requirement.md)
- [Quality Attribute Trade-off](https://arc.fuet.ch/concepts/quality-attributes/architectural-trade-off-thinking.md)
- [Traceability](https://arc.fuet.ch/concepts/principles/traceability.md)
- [Architecture Decision Rationale](https://arc.fuet.ch/concepts/forces-decisions/architecture-decision-rationale.md)
- [Energy Efficiency Tactic](https://arc.fuet.ch/concepts/tactics/energy-efficiency-tactics.md)
- [Architecture Decision Documentation and Requirements Management](https://arc.fuet.ch/concepts/forces-decisions/decision-documentation-and-requirements-management.md)

## Sources

- [TaSSAreCt – Towards Sustainable Software Architectures for CPSoS](https://tassarect.github.io) — tassarect.github.io, accessed 2026-11-09
- [Towards Sustainable Software Architectures for Cyber-physical Systems of Systems (TaSSAreCt) | ZHAW Zurich University of Applied Sciences](https://www.zhaw.ch/en/research/project/76245) — zhaw.ch, accessed 2026-11-09
- [Towards Sustainable Software Architectures for Cyber-physical Systems of Systems](https://alexandria.unisg.ch/entities/funding/4c47be0e-9009-407c-a004-6c9062022a38) — alexandria.unisg.ch, accessed 2026-11-09