Appendix B — Engineering Moves

Appendix B — Engineering Moves

This appendix shows how the same engineering judgment can produce different mechanisms in different systems.

Each section starts from a recurring engineering problem, names the move that addresses it, and shows two realizations.

Read each page in one direction:

Problem → Move → two realizations.

A move is portable engineering judgment: close an action surface, derive obligations from a model, deliver policy where a decision occurs. A mechanism is one concrete realization of that move: a typed mutation API, a coverage census, a context-injection hook. Mechanisms vary by system; the move travels.

Appendix A shows how mechanisms compose into engineering capabilities. This appendix shows how one move can take different forms. The online MAGE Mechanism Catalog contains the broader implementation repertoire.

Figure B-1 maps each recurring problem to its corresponding engineering move.

Figure B.0-1: ten recurring engineering problems, each paired with the move that retires it A two-column cheat sheet. The left column names a recurring engineering cost; the right column names the transferable move that addresses it. Many truths disagree — make one authoritative. Copies drift from authority — derive, don't copy. Model and reality diverge — check correspondence. Assurance has invisible holes — derive the obligation set. Checks are too early or too late — put authority where the property is legible. Actions evade governance — close the action surface. Rules exist but aren't present at the decision — deliver knowledge where the decision occurs. Why gets lost after the change — carry cause with consequence. Operators reconstruct the same procedure — externalize the judgment. Changes have hidden dependents — make dependencies queryable. These are not ten additions to the method; they are recurring realizations of one idea — improve the representation, put authority where obligations are decidable, and make useful judgment durable. Problem → Move ten recurring problems and the engineering move that addresses each RECURRING PROBLEM ENGINEERING MOVE B.1 many truths disagree MAKE ONE AUTHORITATIVE B.2 copies drift from authority DERIVE; DON'T COPY B.3 model and reality diverge CHECK CORRESPONDENCE B.4 assurance has invisible holes DERIVE THE OBLIGATION SET B.5 checks are too early / too late PUT AUTHORITY WHERE LEGIBLE B.6 actions evade governance CLOSE THE ACTION SURFACE B.7 rules exist but aren't present DELIVER KNOWLEDGE AT DECISION B.8 rationale is lost after change CARRY CAUSE WITH CONSEQUENCE B.9 operators reconstruct procedure EXTERNALIZE JUDGMENT B.10 changes have hidden dependents MAKE DEPENDENCIES QUERYABLE
Figure B-1. Ten recurring engineering problems and the moves that address them. The moves apply the method developed in Parts II–IV: model knowledge people repeatedly reconstruct, give decidable obligations authority, and make recurring judgment durable when doing so is worth the cost.
© James C. Davis, 2026–present