Functional Analysis-concept and tools

As mentioned in the previous post ,functional analysis is a method to define the needs the product has to answer and to help experss the specifications.

Functional analysis tools

The “animals with horn” is a tool to help the user to define the specifications.
The head of the animal represents the product to be designed.
Two horns have to answer the two questions: Who is the beneficiary of the product? And Which interactors are concerned?
The tongue of the animals define for what the product is defined.
This tool permits to question the problem about the product itself, the market, the context of the project and the objectives


A Function represents an action of a product or one of its elements only express in term on finality
A service function: is an action requested to a product to satisfy a part of the customer needs. The service functions include:

  • The Interaction functions
  • the Adaptation functions
  • The external point of view is the view of the customer or the user

The whole service functions expressed from an external point of view contributes to the functional wording of the need


The diagram of interactors also called octopus diagram represents the service functions. The product to design is in the center of the diagram., and the external elements (EE) of the environment are positioned around.
An interaction function links to external elements through the product.
An adaptation function links directly an external element to the product.
One diagram has to be defined for each step of the cycles for the use.

A constraint is a characteristic, an effect or an arrangement of design that is mandatory or that has been forbidden for any reasons.
We distinguish the external constraint that concerns finality and that characterizes the relations the product maintains with its environment.
And the internal constraint that concerns the solution, qualified as design disposals.
By example, external constraints can be expressed for the market, the customer, and internal constraints are for the solutions or the technical strategy.

Wording the functions is done with the definition of The goals: why, which goals to assure this function? Is the need really exist? What could provoke the evolution of the function?
And the causes: Why, What are the needed reasons for this functions? What could do that theses goals and causes disappear?


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