Design Thinking in Complex Systems: How UX, UI, and Interaction Designers Each Play a Distinct Role
In today’s most complex environments—healthcare, logistics, finance, defense—digital tools are not just apps or dashboards. They’re decision-support systems. They must align with workflows, meet regulations, and serve expert users under pressure. That’s why design thinking is critical. It offers a human-centered, structured approach to solving problems that affect real lives.
But within that process, different design roles contribute in different ways. While terms like UX, UI, and interaction design are often used interchangeably, they reflect unique skill sets and responsibilities, especially in the context of complex system design.
Let’s walk through the design thinking process—and clarify how UX designers, UI designers, and interaction designers each bring value at every step.
Phase 1: Discovery
Understanding People, Workflows, and Problems Before Building Anything
This first step in design thinking is about empathy: observing, listening, and learning about the people using a system and the context in which they operate.
- UX Designer’s role:
UX designers lead this phase. Their focus is on understanding the user’s journey, pain points, and motivations within the broader system. In a hospital, for example, this might mean shadowing nurses or mapping the end-to-end flow of patient discharge to identify friction points. - Interaction Designer’s role:
Interaction designers begin to shape mental models of how users make decisions, move through systems, and transition between states. They sketch early flow diagrams or interaction maps based on field observations. - UI Designer’s role:
They may help visualize research findings or assist in making research reports more apparent, but they are not yet focused on screen design.
The Discovery phase is about uncovering user needs and system realities—not visual design.
Phase 2: Ideate
Generating Ideas and Concepts Grounded in User and System Insight
Once the problem space is well defined, it’s time to brainstorm solutions. The ideation phase explores a wide range of possibilities—ideally without jumping to finished designs too early.
- UX Designer’s role:
UX designers frame ideation sessions using personas, scenarios, and user needs uncovered during research. They help define constraints (e.g., regulatory rules, user roles, or data flows) so that ideas remain practical. - Interaction Designer’s role:
They sketch possible workflows, decision trees, and behaviors—how the system should respond to user actions, how states change, how one screen flows to the next. They prototype interactive sequences, not just static screens. - UI Designer’s role:
UI designers may join ideation sessions to begin thinking about layout, hierarchy, or visual affordances. However, their core contribution comes in the next phase.
Ideation is where the “what ifs” get shaped into concepts.
Phase 3: Develop
Prototyping, Testing, and Iterating to Explore Viability
This is where ideas become testable. In complex systems, prototypes often simulate decision points, data inputs, alerts, and task flows.
- UX Designer’s role:
UX designers help structure usability testing. They work closely with domain experts to ensure the prototype captures the real-world task accurately. They’re asking: Does this design actually help the user do their job better? - Interaction Designer’s role:
Interaction designers focus on the logic of flows. They refine the timing, feedback, transitions, and contingencies within the system. Their work often includes wireframes or clickable prototypes that simulate behaviour, even before visual design is applied. - UI Designer’s role:
UI designers take rough wireframes and bring them to life. They apply design systems, visual hierarchy, typography, accessibility principles, and interaction cues (e.g., button states, visual feedback). They ensure the system is not just usable, but intuitive and visually coherent.
In development, each designer works in parallel—refining the experience from different angles.
Phase 4: Implement
Building and Evolving the Final Product
Design thinking views implementation not as a final step, but as a continuation of learning. In complex domains, the solution must be tested, adapted, and supported in the wild.
- UX Designer’s role:
UX designers continue to gather feedback from real-world usage. They work with product managers, engineers, and users to adjust features based on outcomes and evolving needs. - Interaction Designer’s role:
Interaction designers collaborate with developers to ensure the behaviour of the system aligns with the intended experience. They help translate flows into functional specifications and test edge cases. - UI Designer’s role:
UI designers partner with front-end engineers to ensure fidelity to the design system. They refine visuals as the product moves from staging to production—fine-tuning, spacing, responsiveness, and accessibility.
Implementation isn’t just handoff it is a collaborative effort.
Quick Summary: Who Does What?
| Phase | UX Designer | Interaction Designer | UI Designer |
|---|---|---|---|
| Discovery | Leads user research and journey mapping | Maps workflows and decision models | Minimal involvement |
| Ideate | Frames problems, defines constraints | Sketches flows and logic | Begins layout thinking |
| Develop | Designs tests, refines user needs | Prototypes behavior | Applies visual design |
| Implement | Validates and adjusts based on usage | Supports implementation logic | Polishes UI and supports dev |
Final Thought: Designing for Complexity Is a Team Effort
In simple apps, the lines between UX, UI, and interaction design may blur. But in complex systems, the differences matter. Each role adds a distinct layer to the final product:
- UX designers make sure the product solves the right problems.
- Interaction designers make sure the system behaves the right way.
- UI designers make sure the product looks and feels right to use.
Together, they transform insights into interfaces—and complexity into efficiency.