P1P2Q1Q2

P1P2Q1Q2 is a label used across several domains to denote a four-part sequence comprising two preliminary or preparation steps, labeled P1 and P2, followed by two evaluation or querying steps, labeled Q1 and Q2. The construction is not a standardized term with a single fixed meaning; its exact interpretation depends on the discipline and context. In manufacturing and quality assurance, P1 and P2 commonly represent preparatory processes or setup tasks, while Q1 and Q2 denote quality inspections or verification checks applied after production steps. In computer science and data analysis, P1 and P2 may stand for probe or preprocess phases, and Q1 and Q2 for queries, tests, or validation steps, with the order indicating a pipeline flow. The notation is favored for its compactness in diagrams, algorithms, and experimental plans, allowing quick reference to the sequence without enumerating each step. Researchers may adapt the labels to fit project-specific semantics, sometimes reinterpreting P as "phase" and Q as "query" or "check," but the numeric subscripts (1, 2) retain their relative order. Limitations of the notation include potential ambiguity if the same labels are used differently in parallel components or if the steps are not strictly sequential. See also workflow, protocol design, and sequential model.