Diagrams Every BA Should Know

Diagrams are how a BA makes the invisible visible. A process living only in people's heads is impossible to improve; drawn on a page, its bottlenecks and gaps become obvious. But each diagram type answers a different question, and using the wrong one creates confusion rather than clarity.

Here is the map. Each of these has its own lesson — this page is the overview that tells you which to use when.

Process & flow

• Flowchart — shows the steps in a process and the decisions along the way. Use it when the question is "what happens, in what order, and what decisions branch the path?" Full lesson →
• Swimlane diagram — a flowchart split into lanes by who does each step. Use it when "who is responsible" matters as much as "what happens."

Behaviour & interaction

• Use case — describes how a user interacts with a system to achieve a goal, including alternatives and exceptions. Use it for detailed system behaviour. Full lesson →
• Sequence diagram — shows the order of messages passed between parts of a system over time. Use it when timing and order of interactions matter.
• State machine — shows the states something can be in and how it moves between them. Use it for things with a clear lifecycle, like an order or a support ticket.

Data & structure

• Entity Relationship Diagram (ERD) — shows what data exists and how it relates. Use it when you need to understand or validate the data behind a system. Full lesson →

Planning & analysis

• Gantt chart — shows tasks against time, with durations and dependencies. Use it for scheduling and timeline planning. Full lesson →
• Fishbone (Ishikawa) diagram — shows the possible causes of a problem grouped by category. Use it for root-cause analysis. Full lesson →
• Mind map — shows ideas branching from a central topic. Use it for early-stage brainstorming and organising thoughts.