47 (3) System requirements, however, go beyond system behavior, describing also the properties and attributes a solution will have (e.g., availability performance, usability, portability, robustness, etc.), and the design constraints to which the project wilt be subjected (e.g., technology or regulatory limitation). Such aspects are collectively referred to as non functional requirements. Green ICT policies typically add non-functional requirements to software projects, imposing new demands in terms of quality attributes that become necessary or desirable, and also establishing new constraints.