Although many definitions of services have been proposed in Service Science and Service Engineering, essentialities of the notion of “service” remain unclear. Especially, some existing definitions of service are similar to the definition of function of artifacts, and there is no clear distinction between them. Thus, aiming at an ontological conceptualization of service, we have made an ontological investigation into the distinction between service and artifact function. In this article, we reveal essential properties of service and propose a model and a definition of service. Firstly, we extract 42 properties of service from 15 articles in different disciplines in order to find out fundamental concepts of service. Then we show that the notion of function shares the extracted foundational concepts of service and thus point out the necessity of the distinction between them. Secondly, we propose a multi-layered model of services, which is based on the conceptualization of goal-oriented effects at the base-level and at the upper-level. Thirdly, based on the model, we clarify essential properties of service which can distinguish artifact function. The conceptualization of upper-effects (upper-service) enables us to show that upper-services include various effects such as sales and manufacturing. Lastly, we propose a definition of the notion of service based on the essential properties and show its validity using some examples.
