# Chapter 1 ## Functional and non-functional properties Techniacal systems are described using two types of characteristics: __Functional properties:__ Which functions are performed. __Non-functional properties:__ How well these functions are performed. These terms can be used to describe systems, let's say a car: The primary function of a car is to transport people and goods from one place to another. Non-functional properties include the carrying capacity, the maximum speed, whether the car starts when needed, whether it transports people and goods to destination without breaking down or causing accidents. These are the _performance_ (carrying capacity, speed) and _dependability_ (the car starts and fulfills its function) properties of the system. Along with the price they are rational arguments for comparing different designs. When designing an ICT-system, the focus is mainly on the functions the system shall provide and how to implement them. However, in a real system, it is also crucial to concider non-functional properties such as dependability and performance. The non-functional requirements will have an impact on both the design and the cost of the system and determine its usability.