AP242 Fourth Edition Changes

Overview

The fourth edition of AP242, published in August 2025 contains enhancements for datum sets and tolerance modifiers as well as a variety of new definitions.

This builds on the third edition, which added new definitions for presentation, features, and model associativity, the second edition, which introduced many definitions for semantic tolerances, additive setup, improved tesselated models and point cloud data, and the first edition, which added kinematics, assembly constraints, and PMI, beyond what AP214 and AP203e2 could originally handle.

Programming Notes

The fourth edition contains no changes to entity attributes as defined by the previous edition. Code written against the last version should not require any changes to existing logic.

The AP242 schema name has not changed between editions, so the StplibSchemaType stplib_schema_ap242 enum is still used to identify all AP242 files.

RoseDesign * d;

// schema name "AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF"
stplib_put_schema (d, stplib_schema_ap242);

switch (stplib_get_schema(d)) {
case stplib_schema_ap242:
    // ap242 E1/E2/E3/E4
}

When writing new files as AP242, we append the fourth edition ASN/1 version identifier to the schema name. You can examine the original schema name string found in the STEP Part 21 file with stplib_get_schema_name() or change it with stplib_put_schema_name()

 { 1 0 10303 442 1 1 4 }   ASN/1 for first edition
 { 1 0 10303 442 3 1 4 }   ASN/1 for second edition
 { 1 0 10303 442 4 1 4 }   ASN/1 for third edition
 { 1 0 10303 442 5 1 4 }   ASN/1 for fourth edition

New Entity Definitions

The fourth edition of AP242 extends PMI capabilities with new tolerance modifiers, allowing shape aspect relationship to be a tolerance target, allowing a set of repitems as a styled item target, and the following suptypes for a group tolerance and composite data system:

The following enumerators were modified:

datum_reference_modifier_type: values reordered
directed_tolerance_zone_type: values reordered, add angular, and symmetrical_to.
geometric_tolerance_modifier: values reordered, add continuous_features, derived_feature, each_element, individually, offset_zone, separate_zones, stock, unspecified_angular_tolerance_zone_offset, unspecified_linear_tolerance_zone_offset, and variable_angle.
simple_datum_reference_modifier: values reordered

The 203 entities listed below were added for new geometry types, experience, person-in-organization, risk, and other purposes. Not listed here are 71 other entities added for reporting various data quality issues.