EXPRESS (ISO 10303-11)

EXPRESS is the formal data-modeling language defined in ISO 10303-11 — the language used to write every Application Protocol (AP) schema in the STEP family (10303-203, -214, -242, etc.). It is to STEP what XML Schema is to XML or what UML is to OO software: the meta-language in which the data shapes are declared.

Scope

• Entity types, attributes, and inheritance — schema declarations.
• Domain and uniqueness rules — formal constraints on populations.
• Aggregations — set, list, bag, array of entities.
• WHERE rules — first-order-logic constraints over instances.
• EXPRESS-G — graphical notation for EXPRESS schemas.
• EXPRESS-X / Part 14 — schema mapping language between EXPRESS schemas.

Why it matters

Every STEP-AP file (.stp, .step, .p21) you receive from a CAD vendor has an EXPRESS schema as its contract. PLM integrators who write STEP processors, validators, or AP242 mappings need EXPRESS literacy. The schema also drives the more recent STEP XML / Part 28 encodings.

Relationships (see sidebar)

• Normative for STEP AP242 Data Exchange (and every other STEP AP) and for canonical PLM Data Models that derive from STEP integrated resources.

Steward

ISO/TC 184/SC 4 (Industrial automation systems and integration — Industrial data).