The importance of cost engineering within Product-Service Systems (PSS) discipline has increased in recent years. Literature reveals that there is a need for holistic PSS cost determination approaches dealing both with PSS cost engineering and PSS functional uncertainty - as a System of Systems (SoS), as PSS cost determination uncertainty arises from the limited understanding of PSS behavior as a SoS. This work proposes a System Quality Attributes (SQA) Ontology developed to measure the function of a PSS: How well it performs in light of its intended purpose? The PSS-SQA Ontology was constructed on the foundations of SoS Engineering and Reliability Engineering disciplines. It propose a holistic approach to PSS functional measurement, covering the most accepted PSS typology, including product-, use- and result-oriented PSSs. The work contributes to PSS engineering by offering an SQA Ontology that quantifies PSS functionality and reduces PSS functional uncertainty for further cost determination.