Product structure modeling

Introduction

Product structure [modeling] is a hierarchical decomposition of a product, typically known as the Bill of Materials (BOM).

—Wikipedia, 

Domain Theory

Domain Theory is a systems approach for the analysis and synthesis of products. Its basic idea is to view a product as systems of activities, organs and parts and to define structure, elements, behaviour and function in these domain.

—Domain Theory, Its Models and Concepts, 

According to Domain Theory, a product is seen from four system point of views:

• A process view, where the transformation of materials, energy, and information of the product related to its use or function is central. This viewpoint lead to description of a process structure.
• An effect view, where the desired functions or effects are in focus. These effects must be able to facilitate the necessary transformations. This viewpoint is related to an effect / function structure.
• An organ view, where the technical principles or means of the product are in focus. These principles or solutions are called organs (or function carriers) and by their functionality they create the desired effects. The result of design considerations is an organ structure.
• A part view (or assembly view), where the machine parts of the products are in focus. By determining material, form, tolerances and surface quality of each part and relations between the parts, the necessary conditions for the organs and their functionality are created.

Function-oriented decomposition

Each of the four structural views indicates possible ways of decomposing a product or product assortment. Functional decomposition seems to be the core of decomposition because it can be argued that functionality is the most important property of a product, i.e. if the product does not possesses right functions then other properties are uninteresting.

A function-means tree for a tumble dryer, Hansen

Product-Function-Component tree

Product-Function-Component tree is rooted with product on the top of the tree, and then a merge of functions to next tree-level is made. Since in this stage we know nothing about product sub-systems or subassemblies, i.e. we know nothing about product’s component structure we assign functions to the second-tree level so they will substitute product’s subsystems. Assumption made here is that a product can be broken down into subassemblies corresponding to the functions of the technical system. According to this, Product-Function-Component tree is created by merging two dependant tree structures.

Functional Decomposition Digrams

Typically, functional decomposition is used during the project analysis phase to create functional decomposition diagrams (FDDs), as part of requirements specification documents. However, it can also be used for smaller projects, to document the deliverables and to clarify whether the project is on the right track.

When dealing with functional decomposition, it pays off to have a good knowledge of some basic terms associated with it:

Function – A function is a task expressed as a verb-noun phrase. Some examples of the functions of ATM machines are verb-noun phrases such as “reads cards,” “prints recipes,” or “allows for touch input.” Sub-function – Functions often have a hierarchical relationship. This means that certain functions require other functions to work in order to be executed. The required functions are sub-functions of a higher function. Decomposition – Decomposition is the process of breaking down something complex into smaller parts. FDD (functional decomposition diagram) – The individual functions and sub-functions of a process or system can be graphically displayed in a hierarchical order as a functional decomposition diagram, which shows how the various functions are organized.

How To Perform Functional Decomposition

When designing a system using the functional decomposition approach, start by identifying a single general function that best encapsulates the major objective. Try to avoid accidentally including secondary functions in the definition of the general function to keep the functional decomposition process as unrestricted as possible.

Keeping the general function in mind, proceed to find the closest sub-functions that must happen in order for the general function to take place. Think about how the sub-functions connect to the main function and note it down in a functional decomposition diagram.

Continue like this sub-function by sub-function, trying to find other required sub-functions. Repeat this until you’ve identified all required sub-functions. Finally, carefully check the resulting functional decomposition diagram for errors and inaccuracies.

See Also

• Wikipedia - Function–means tree