"Meet Requirements" is not a Valid Function

To begin with, Meet Requirements is what a design is required to accomplish.  A function is a "Verb-Noun" relationship which leaves a design item and is needed by the next item in the sequence or by the customer.  The causes of failure to meet requirements will include all inputs, the entire scope of the design, and will have very little structure to analyze.  It will provide a "mind dump" of mostly useless information along with a few pearls of wisdom. 

On a cold winter morning, most people love the "Heat Steering-wheel" function.  But, how much is too much...how little is too little?  What are the requirements?  Warm the hands?  How much?  How much is too much?  How little is too little?  These are the requirements.  Does the amount of energy used to heat the wheel depend on the temperature in the cabin of the vehicle?  With "Meet Requirements, " what is missing is the primary function which has the designed purpose to satisfy stated requirements.  What are the components that produce the design? How do these items have to work together to produce, transfer, and regulate heat?  These are the design items over which the engineer will make a decision.  These produce the functions that have to work together and have to "meet requirements."

The energy/time sequence needs to be understood.  Knowing that a Thermal Heating Element has a function "generate heat," you can talk about how long is the element, how wide is the element, how much current is needed?  How will the current be produced?  What is the current in to heat out transfer function?  Regarding the supporting functions, how will the current be controlled (stop/start, magnitude).  How will the element be positioned?  How will it be held in place?  How will current be transferred to the heat element?  Will the heat start automatically under some conditions and be manual  for other conditions?  I love that when my car is cold in a parking lot, the heat goes on automatically.  What is the scope of the design decisions which need to be made?

In the Design Tree Diagram it can be seen that Super Systems are produce by systems working together.  Systems are produced by assemblies working together.  Assemblies are produced by parts working together.  A part function is controlled by dimensions.  Dimensions are supported by material characteristics.  Energy enters material, is focused by dimensions, produces the function required by other parts and the next higher level function is the  primary function of the lower level structure.  This continues up to the Super System.  At every level there are position, hold, and dimension interface functions as the structures are joined together.  Each level has its own specified requirements for the function at its specific level.

It is best to analyze one level of the design at a time.  Functions have a geometrical growth rate of a minimum 10 functions as you move down the tree towards energy (e.g. 10 functions at one level become 110 one level down - 10 plus the 100 growth).  Most multilevel studies are unwise as the majority of teams max out their abilities at around 50 functions.  It takes roughly 1 hour to really study and understand each function.  This is why systems are broken into subsystems and assemblies are broken into subassemblies.

Back to the main point, which is why requirements are not valid functions.  If one of the In scope functions were actually a requirement, where would it fit on the following functional block diagram?

The answer is, "It would not."  One of the functions would likely relate to a requirement.  It is most likely that the Primary Function would relate to the requirements for the design.  In the functional block diagram, the quality of the function is judged against the need of the following design item.  Each function has four specific types of specifications which are useful.  The conversation for the quality of the functions, which address the requirements for the function is lengthy and I will post another article at a later date.

Clearly understand that the requirements relate to how the customer will perceive the quality of functions and need to link the quality of the function to the customer.  The most important requirements are those which will directly impact the customer.  the most important functions are those which will be judged by these requirements.