Developing a
Function-Means Tree
What functions will the design
have? By what means will those
functions be achieved?
Taken from engineering design: a project-based introduction by dym & little
It helps to go beyond the terminology and to
know what you’re really trying to do.
• Think of the “functions” as what you must do.
• Think of the “means” as how you might do it.
• The Function-Means Tree is a tool for listing the
primary functions of a design and various means of
achieving those functions.
• The Function-Means Tree should flow out of the
Attributes List, PCC, Objectives-Constraints Tree,
and Design Specifications.
Before you start too far down the path of
“brainstorming” various design alternatives…
• Determine the primary functions that are required.
– Show these on the top level of the tree
• List various means by which each function may be
implemented.
– Show these on the next level of the tree
• Determine secondary functions that would result
from implementing each of the means.
– Show these on the next level of the tree
• The tree continues to alternate between means and
functions until you reach a reasonable termination
point.
Here is a partial Function-Means Tree for a
cigarette lighter.
IGNITE
LEAFY
MATERIALS
Primary function
Secondary functions
Electrically
Heated
Wire
Convert
electricity
to heat
Generate
electric
current
Apply heat
to leafy
materials
Focused
Sunlight
Protect
users from
post-usage
burns
Laser
Possible means of achieving
the primary function
Flame
Store fuel
Control
flame
Supply fuel
for flame
Ignite fuel
Butane
Miniature
heat pump
Resistive
wire
Spark
Wall-outletbased system
Control
electrical
current
Battery-based
system
Store
electricity
Gasoline
Electrical
resistance
Secondary means
Convert chemical
energy to
electrical current
Protect
electric
current from
flame
Generate
electric current
Function
Tertiary functions
Means