A requirements data model for product service systems

Product service systems (PSS) are bundles of physical technological elements and service elements that are integrated to solve customer problems. In practice, most components of PSS are developed independently from each other, which leads to problems with coordination of development activities and integration of PSS components. Therefore, an integrated requirements engineering for PSS is needed that deals with the involvement of developers from product engineering, software engineering, and service engineering, as well as the inherent complexity of the PSS and the development process. In a case study with the development department of a PSS provider, we analyzed requirements documents and conducted expert interviews. We identified problems in the development, for example, that requirements on different levels of abstraction are intermingled, rationales for requirements are missing, and the concretization of requirements is unclear. To solve these problems, we propose a requirements data model (RDMod) for requirements to PSS. An RDMod describes different types of requirements and the relations between them. Thus, it is a scheme for the concretization of the requirements, which especially addresses the problems of structuring the requirements, enabling traceability, and finding conflicts. We then used an analytical evaluation, a feature-based evaluation and a retrospective application with requirements analysts of the industry partner. In a joint workshop, we specified requirements for a PSS with the RDMod. In structured interviews, we analyzed the perceived advantages of the RDMod. The experts confirmed that the RDMod is applicable in their development and it provides a clear structure for the requirements and therefore helps overcoming the identified problems.