Institute of Electrical & Electronic Engineers
A service system's quality is multifaceted, including functional and nonfunctional technical aspects, as well as nontechnical aspects ranging from business to social characteristics. Elasticity is a good example of this multifaceted quality: it describes a system's capacity to add or remove various resources as needed to efficiently operate in a fast and convenient manner and without severe impact on other qualities, such as system availability or performance. Units make the usage and properties of diverse resources, including infrastructure and human resources, explicit early in system design, and allow for reasoning about complex system qualities, such as elasticity. They advance the measurability and management of systems whose quality depends largely on the resources that the system uses.