Functional Decomposition for Business Analysts (Phân rã chức năng)

What it is

Functional decomposition breaks a complex whole into smaller, manageable parts until each part is small enough to understand, estimate and build. BABOK v3 technique 10.22.

System
└── Module (business capability)
    └── Feature
        └── Function (atomic action)

When to use

• At the start of a project, to agree on scope with stakeholders.
• Before estimation — each leaf function can be sized.
• As the backbone of a traceability matrix (function ID → user story → test case).
• When taking over a legacy system with no documentation.

Rules of thumb

1. MECE — Mutually Exclusive, Collectively Exhaustive. No overlaps, no gaps.
2. Group by capability, not by screen. “Payment” is a capability; “Checkout page” is a screen.
3. Verb + noun names: “Approve leave request”, not “Approval”.
4. CRUD check each business object — missing “Cancel booking” is a classic gap.
5. Remember cross-cutting functions: login, roles, notifications, audit log, reports, master data.

Sai lầm thường gặp

• Trộn phân rã chức năng (cấu trúc cây) với quy trình (thứ tự các bước).
• Phân rã theo phòng ban/team thay vì theo năng lực nghiệp vụ.
• Dừng quá sớm ở mức “Quản lý X” mà không liệt kê chức năng con.

Practice

Ask Claude: “Phân rã chức năng cho ứng dụng đặt lịch khám phòng khám” and check the CRUD table for gaps.

Use this with Claude: install the plugin with /plugin marketplace add lechithinh/ba-claude-skills, or read the skill source on GitHub.