How do you apply functional analysis and decomposition to define design requirements and specifications?

1 What is functional analysis?

Functional analysis is the process of identifying and describing the functions that your product or system needs to perform, and how they relate to each other and to the environment. A function is a specific action or task that contributes to the overall purpose or goal of the design. For example, a function of a bicycle is to provide propulsion, while a function of a coffee machine is to brew coffee. Functional analysis helps you define the scope, objectives, and criteria of your design problem, and avoid unnecessary or conflicting functions.

2 What is functional decomposition?

Functional decomposition is the process of breaking down a complex function into simpler and more manageable sub-functions, until you reach the level of detail that is sufficient for your design. A sub-function is a function that supports or enables a higher-level function. For example, a sub-function of providing propulsion for a bicycle is to transfer power from the pedals to the wheels. Functional decomposition helps you organize and structure your design problem, and identify the components, interfaces, and interactions that are required for your product or system.

3 How to perform functional analysis and decomposition?

A functional model is a graphical representation of the functions and sub-functions of a product or system, and their associated inputs, outputs, and dependencies. To create one, you can begin by writing the main purpose of your design as a verb-noun phrase, such as "provide propulsion for a bicycle". Then, identify the inputs and outputs of the main function, and the sub-functions that are necessary to achieve it. Continue this process until you reach the desired level of detail. Finally, arrange the functions and sub-functions in a logical order and hierarchy and connect them with arrows to show the flow of inputs and outputs. This will create a functional block diagram or function tree.

4 How to use functional analysis and decomposition for design requirements and specifications?

Functional analysis and decomposition can help you define the design requirements and specifications for your product or system, by translating the functions and sub-functions into measurable and verifiable parameters. Design requirements are the constraints and criteria that your product or system must satisfy, such as performance, reliability, safety, cost, etc. Design specifications are the detailed descriptions of the features and characteristics of your product or system, such as dimensions, materials, components, etc. To use functional analysis and decomposition for design requirements and specifications, consider the following steps: identify relevant design requirements for each function and sub-function; define appropriate metrics and units to measure them; identify possible design specifications; estimate expected values or ranges of metrics; and select the best design specification based on comparison of metrics with target values or ranges. Additionally, consider factors such as feasibility, availability, cost, etc. when making your selection.

5 How to improve your functional analysis and decomposition skills?

Functional analysis and decomposition are skills that can be improved with practice and feedback. To enhance these skills, you should use a systematic and iterative approach, such as the one described above. Additionally, use appropriate tools and techniques, like diagrams, tables, matrices, checklists, etc., to visualize and document the functional model and design requirements. Furthermore, learn from examples and case studies of other designers who have applied functional analysis and decomposition. Lastly, seek feedback from peers, mentors, clients, users, etc., on the functional model and design requirements. Collaborating with other designers who have different perspectives can also be beneficial for learning more about functional analysis and decomposition approaches.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?