Functional decomposition is a business analysis technique that breaks down the business goals into smaller and more manageable objectives and measures. It helps to identify the scope, requirements, and deliverables of a project or initiative. Functional decomposition can also be used to analyze the current state and the desired future state of a business process or system. References:
Business Analysis Expert Certification, CCBA® | IIBA®, section "CCBA Competencies" Certification of Capability in Business Analysis (CCBA®) - Simplilearn, section "Business Analysis Planning and Monitoring"