Types of Customer Requirements and the System Architecture Process

There are two types of customer requirements: functional and design constraints.

Functional requirements are the "must perform" requirements. 

• "The wing on an aircraft must provide 10 tons of lift when configured for takeoff." 
• "The refrigeration must keep food below 40 degrees, but above 32 degrees Fahrenheit."
• "The kitchen faucet must allow for convenient cleaning of large pots."

Design constraints are the "must meet" requirements. "

• "The USB port on the computer must meet the current USB port standards."
• "The application must have two factor authentication."
• "The electric motor must operate using standard 60 cycle, 110 volt current."

The System Architect decomposes the customer's functional requirements and derives the functions the tool or system needs.  Then structures and orders these functions into a System Architecture that may be called a functional design.  The System Architect subsequently allocates the tool's or system's functions to components.

However, the design constraints are not part of the system architecture.  Instead, the System Architect simply allocates these to the components at the time he or she allocation the functions.

Using this System Architecture process will greatly reduce the complexity of complex implementation and transformation efforts, which significantly reduces the probably of failure of the effort