[Context and motivation] Service Management has been steadily gaining in importance in many organizations and is becoming a major force of change in IT departments. ITIL, one of the main service management frameworks, defines the value of a service for its customers as the sum of the service utilities and service warranties but provides no specific rules for defining them. [Question/problem] Companies, IT departments and their consultants face difficulties defining utilities and warranties, as well as identifying their value for customers. [Principal ideas/results] We propose a general framework for understanding service requirements and for analyzing the quality of a service. The framework is based on General Systems Thinking. We define service utilities as norms created by the service for a given stakeholder. Service warranties then protect the stakeholder from variations of these norms as a result of threats. Value is created when the norms are maintained within the tolerance range of the stakeholder. Risk is defined as the possibility of detrimental consequences for a stakeholder if the norm is pushed outside its tolerance range. [Contribution] We believe that this work has the potential to advance theory and practice of service management in both academia and industry, and to reduce the risk of overlooking important service properties when defining service requirements.