Sub-systems identified:

• Ball releasing unit
• Obstacle control unit
• Interface unit
• Ball transfer unit

Interface performance specifications

Subunit	Flow	Obstacle control unit	Interface unit	Ball transfer unit	Justification
Ball releasing unit	Material flow	Yes	No	Yes	There is material flow from ball releasing unit to the other two units, but not to the interface unit
	Data flow	Yes	Yes	No	There is data flow from ball releasing unit to the other two units, but not to the ball transfer unit
	Spatial flow	Yes	No	Yes	There is spatial flow from ball releasing unit to the other two units, but not to the interface unit

Subunit	Flow	Ball releasing unit	Interface unit	Ball transfer unit	Justification
Obstacle control unit	Material flow	Yes	Yes	Yes	There is material flow from obstacle control unit to the other three units
	Data flow	Yes	No	No	There is data flow from obstacle control unit to the ball releasing unit but not with other units
	Spatial flow	Yes	No	Yes	There is spatial flow from obstacle control unit to the other two units, but not to the interface unit

Subunit	Flow	Ball releasing unit	Obstacle control unit	Ball transfer unit	Justification
Interface unit	Material flow	No	Yes	No	There is material flow from interface unit to the obstacle control unit but not with other units
	Data flow	Yes	Yes	Yes	There is data flow from interface unit to the other three units
	Spatial flow	No	No	Yes	There is spatial flow from interface unit to the ball transfer unit, but not to the other two units

Subunit	Flow	Ball releasing unit	Obstacle control unit	Interface unit	Justification
Ball transfer unit	Material flow	Yes	Yes	No	There is material flow from ball transfer unit to the two units but not with interface unit
	Data flow	No	No	Yes	There is data flow from ball transfer unit to the interface unit but not with the other two units
	Spatial flow	Yes	Yes	Yes	There is spatial flow from ball transfer unit to all the three units