cad-cross: 土木・機械・建築の CAD 形式は同じ ISO 10303-21 だった

Civil engineering (SXF), mechanical engineering (STEP AP242) and architecture (IFC) are treated in practice as three separate CAD worlds, each with its own tools and its own specialists. They are not. All three are ISO 10303-21 (STEP Part21). This is demonstrated rather than asserted: the parser written for IFC in bim-bench is applied, byte-identical in its executable code (verified by SHA-256 at run time), to the other two industries. One parser reads 54 files and 762,430 entities across all three. The vocabularies, however, do not overlap. Measured by type name, civil and architecture share 0 types; mechanical and architecture share 0; all three share 0. Measured by concept — stripping the IFC prefix and the underscores that AP202/AP242 retain — all three share 6: point, direction, polyline, colour, coordinate context, styled item. CARTESIAN_POINT and IFCCARTESIANPOINT are the same concept under different names. The container is shared and the lowest layer of geometry is shared. What separates the industries is a namespace, and for a machine reader that wall is one line of string handling. The real barrier sits above it, in the vocabulary of meaning — tolerances, spatial hierarchy, drawing elements — where domain knowledge is genuinely required. Civil coverage is saturated: all 20 published P21 drawing examples across 7 structure types were measured, and the type vocabulary grew only from 64 to 70 as the data grew tenfold. 土木SXF・機械AP242・建築IFCは同じ ISO 10303-21 の器に入っている。1つのパーサで 3業界76万実体を読み、語彙は型名で全く重ならないのに概念では6種重なることを示した。 業界を分けていたのは形式ではなく名前空間だった。