The attributional life cycle inventory modelling principle is also referred to as "accounting”, “book-keeping”, “retrospective” or “descriptive” (or sometimes and potentially confusing: “average” or “non-marginal”). It depicts the potential environmental impacts that can be attributed to a system (e.g. a product) over its life cycle, i.e. upstream along the supply-chain and downstream following the system's use and end-of-life value chain. Attributional modelling makes use of historical, fact-based, measureable data of known (or at least know-able) uncertainty, and includes all the processes that are identified to relevantly contribute to the system being studied. In attributional modelling the system is hence modelled as it is or was (or is forecasted to be).