in which transportation can be achieved simultaneously (as in car-pooling); one in which transportation can be achieved sequentially (as in car-sharing); and one in which transportation can be achieved eventually (rent-to-own). Types There are various issues in the nomenclature of the discussion of PSS, not least that services are products, and need material products in order to support delivery, however, it has been a major focus of research for several years. The research has focussed on a PSS as system comprising tangibles (the products) and intangibles (the services) in combination for fulfilling specific customer needs. The research has shown that manufacturing firms are more amenable to producing "results", rather than solely products as specific artefacts, and that consumers are more amenable to consuming such results. This research has identified three classes of PSS: Product Oriented PSS: This is a PSS where ownership of the tangible product is transferred to the consumer, but additional services, such as maintenance contracts, are provided. Use Oriented PSS: This is a PSS where ownership of the tangible product is retained by the service provider, who sells the functions of the product, via modified distribution and payment systems, such as sharing, pooling, and leasing. Result Oriented PSS: This is a PSS where products are replaced by services, such as, for example, voicemail replacing answering machines. This typology has been criticized for failing to capture the complexity of PSS examples found in practice. Aas et al. for example proposed a typology with eight categories relevant in the digital era, whereas Van Ostaeyen et al. proposed an alternative that categorizes PSS types according to two distinguishing features: the performance orientation of the dominant revenue mechanism and the degree of integration between product and service elements. According to the first distinguishing feature, a PSS can be designated as input-based (IB), availability-based (AB), usage-based (UB) or performance-based (PB). The performance-based type can be further subdivided into three subtypes: Solution oriented (PB-SO) PSS: (e.g. selling a promised level of heat transfer efficiency instead of selling radiators) Effect oriented (PB-EO) PSS: (e.g. selling a promised temperature level in a building instead of selling radiators) Demand-fulfillment oriented (PB-DO) PSS: (e.g. selling a promised level of thermal comfort for building occupants instead of selling radiators) According to the second distinguishing feature, a PSS can be designated as segregated, semi-integrated, and integrated, depending on to what extent the product and service elements (e.g. maintenance service,