A product system is a system of consecutive and interlinked Unit processes which models a product life cycle. This definition provides clarity by disentangling the circular references found in ISO 14040 sections 3.1 and 3.34, where "product system" and "life cycle" are defined in terms of each other.
ISO 14040 (clause 3.28) defines a unit process as the smallest element considered in the life cycle inventory analysis for which input and output data are quantified. These unit processes represent individual activities such as raw material extraction, manufacturing steps, transportation, product use, and waste treatment operations. Each unit process transforms inputs into outputs through specific activities.
The product system connects these unit processes in a meaningful sequence that traces the complete journey of a product from cradle to grave. The term "consecutive" indicates that these processes follow one another in a logical temporal and functional order, whilst "interlinked" emphasises that the outputs of one process serve as inputs to subsequent processes, creating a network of material and energy flows throughout the product's life cycle.
This systemic approach is fundamental to Life Cycle Assessment methodology, as it enables practitioners to capture and quantify all relevant environmental exchanges associated with delivering a specified function. The product system serves as the analytical framework within which the functional unit is fulfilled, providing the scope and boundaries for inventory data collection and impact assessment.
By modelling the product life cycle through interconnected unit processes, the product system reveals both direct and indirect environmental burdens, enabling comprehensive assessment of a product's total environmental performance from resource extraction through final disposal or recycling.
