System boundary

A system boundary defines which processes, actors, and flows an analysis includes and excludes. It determines what counts as part of the system and what lies outside it.

System: A set of interacting components considered together as a whole. A boundary separates the system being analyzed from its surroundings.
Control volume: A selected region in space or matter used to track transfers and changes. Its enclosing surface makes system-boundary accounting explicit.
Life cycle assessment: A method for assessing environmental impacts across a product or service life cycle. Its results depend strongly on which life-cycle stages the boundary includes.
Life cycle inventory: A quantified account of inputs and outputs across the processes in a life-cycle assessment. The inventory contains only flows within the chosen boundary.
Externality: A cost or benefit of an activity borne by people not directly involved in it. Externalities arise when consequential effects fall outside a defined system boundary.
System of interest: The system selected for study, design, or management. Its stated scope determines where the boundary is drawn.
Mass balance: An accounting of matter entering, leaving, and accumulating within a system. It requires identifying which material transfers cross the boundary.
Cradle-to-grave: An assessment scope covering a product from raw-material extraction through disposal. It is a broad life-cycle boundary spanning production, use, and end of life.
Burden shifting: The transfer of environmental impacts from one place, life-cycle stage, or category to another. Narrow boundaries can hide impacts shifted beyond the assessed system.
Problem of induction: The philosophical problem of justifying general conclusions from limited observations. Boundary choices can make evidence appear complete while excluding unobserved processes.

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