Who determines the level of decomposition — you yourself or do you coordinate with the team lead and stakeholders? At what level is coordination with the business customer?

The level of decomposition is determined collaboratively: as a systems analyst, you propose an initial structure, but the final decision is made in consultation with the team lead and other technical specialists to ensure feasibility and ease of implementation.

Coordination with the business customer occurs at a higher level — usually involving functional blocks, business processes, or large modules. Detailed technical decomposition is typically discussed within the development team.

Thus, you act as a link between the business and technical team, ensuring that requirements are correctly understood and broken down into manageable parts.