System Architecture and Conceptual Design
Domain 5 tests system architecture and conceptual design: partitioning a system, defining interfaces, allocating requirements, and making structure explicit before detailed design commits cost.
Core rules and concepts
- Architecture is the fundamental organization of a system embodied in its elements, their relationships to each other and to the environment, and the principles guiding its design and evolution.
- Partitioning should reflect cohesion and coupling, changeability, safety, and reuse. Allocation maps requirements to elements and interfaces.
- Interfaces include physical, logical, power, data, and human. Each needs an owner, a specification, and a verification method.
- Conceptual design explores alternatives before commitment. Architecture decisions are recorded with context, alternatives, rationale, and consequences.
Worked example
A satellite ground segment must support new instrument types. A monolithic architecture couples data ingestion to processing, so every instrument change forces regression testing of the whole chain. The team proposes a layered architecture with a published ingest interface and plug-in processing. Reasoning: the anticipated change scenario drives the partition. The interface contract localizes future change and makes the cost of change predictable.
Traps that cost marks
- Treating a single diagram as the architecture.
- Leaving interfaces implicit until integration discovers them.
- Over-partitioning into elements that cannot be integrated or tested.
- Recording a decision without alternatives or rationale.
- Allocating requirements to elements that cannot satisfy them.
Key points
- Architecture includes elements, relationships, and principles.
- Partition for change, cohesion, and safety.
- Interfaces need owners and specifications.
- Record rationale and alternatives.
- Explore concepts before commitment.