FFBD

FFBD stands for Functional Flow Block Diagram, a graphical method used in systems engineering to model the functional behavior of a system. In an FFBD, each function is represented by a block, and connections between blocks are arrows that carry inputs, outputs, or control signals. The blocks are typically arranged to reflect the sequence of operations, often read from left to right to indicate the flow of time or process order. The diagram emphasizes what the system does (functions and their relationships) rather than how it is physically realized, making it useful for functional decomposition, interface definition, and requirements traceability.

Elements commonly shown in an FFBD include labeled functional blocks, incoming arrows for inputs or triggers, outgoing arrows for results or outputs, and optional annotations specifying data types, resources, or conditions. Time sequencing and execution order are implicit in the layout, and blocks can be refined hierarchically to show subfunctions while preserving the overall flow.

Applications and history: FFBDs have been used since the mid-20th century as part of broader systems engineering and requirements analysis, especially in aerospace and defense projects. They are employed during concept development, system integration, and test planning to identify missing functions, clarify interfaces, and allocate functions to components. They are often used in conjunction with other modeling approaches and documentation standards.

See also: Functional modeling, N2 chart, IDEF0, Function allocation.