Anatomy of Product Entities

A detailed look at the attributes required to correctly define product information in a STEP file (Part 21).

Hierarchy Overview

1. PRODUCT

The top-level element defining the part or assembly itself.

ENTITY product;
  id : identifier;              -- 1. Part Number
  name : label;                 -- 2. Display Name
  description : OPTIONAL text;  -- 3. Description (Optional)
  frame_of_reference : SET [1:?] OF product_context; -- 4. Design Context
END_ENTITY;

• id: Must be unique within the implementation context.
• frame_of_reference: Usually refers to a product_context containing 'mechanical' or similar to indicate mechanical design.

2. PRODUCT_DEFINITION_FORMATION

Manages the "version" or "revision" of a product.

ENTITY product_definition_formation;
  id : identifier;              -- 1. Revision ID (e.g., 'A', '1')
  description : OPTIONAL text;  -- 2. Description
  of_product : product;         -- 3. Target PRODUCT
END_ENTITY;

3. PRODUCT_DEFINITION

The definition of a product in a specific context (design, analysis, etc.). This is the starting point for linking to geometry data.

ENTITY product_definition;
  id : identifier;              -- 1. Definition ID (e.g., 'design')
  description : OPTIONAL text;  -- 2. Description
  formation : product_definition_formation; -- 3. Target FORMATION
  frame_of_reference : product_definition_context; -- 4. Life-cycle or other context
END_ENTITY;

Implementation Advice

• Duplicate IDs: In a Part 21 file, multiple entities may have the same id value, but their meanings differ by entity type.
• Reusing Contexts: It is standard practice to define a context once (e.g., #1=PRODUCT_CONTEXT(...)) and reference it from multiple PRODUCT entities.

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📚 Next Steps

• Data Model Map - See how these entities connect to geometry and each other.

Back to README | Back to Data Model Map