System of systems
A system of systems is an architectural composition where independently developed, independently owned, independently operated systems are integrated to produce capability greater than the sum of parts. The systems retain their independence — they continue to evolve, deploy, and operate separately — but coordinate via defined integration contracts.
The pattern emerges in domains where unified ownership is impossible: defence (multiple service branches), healthcare (hospitals, insurers, pharmacies), supply chain (many independent businesses). The architectural challenges are correspondingly different from single-org architectures: contracts must be longer-lived (you can't ask 30 partners to coordinate breaking changes), failure modes are more nuanced (partial-system availability matters), and observability is partial (you see what your contracts allow). The discipline of system-of-systems architecture borrows from microservices (independent services), federated identity (cross-org auth), and event-driven integration (loose coupling via events) without being reducible to any one.
Related terms
- Microservices
Microservices is an architectural style where a single application is composed of many small, independently-deployable services, each owning its own data and communicating over the network.
- Service-oriented architecture (SOA)
Service-oriented architecture is the design approach that structures applications as a collection of services communicating over a network — distinct from monoliths (single application) and microservices (small, independently deployable services).
- Event-driven architecture
Event-driven architecture is the design pattern where services communicate by emitting and consuming events rather than by direct synchronous calls.