Every entity in a CDD dictionary — every class, property, value list, value term, unit, and relation — is identified by an International Registration Data Identifier (IRDI). IRDIs are defined by ISO/IEC 11179-6 and adopted by IEC 61360 as the canonical, language-independent handle for dictionary entries. Two systems that cite the same IRDI are guaranteed to be talking about the same entity.

This page covers what an IRDI looks like, how to parse one, and how to cite one in your own work.

Anatomy of an IRDI

A full IRDI has four parts separated by / and #:

For 0112/2///61360_4#AAD009:

The /// separator is literal: it delimits an empty version field. ISO 11179 allows a version after the second slash, but IEC CDD does not use it; the version lives on the entity itself (the version and revision attributes), not in the IRDI.

The four parts in detail

Registrant

A numeric identifier assigned by the registration authority. Common ones you will see:

Within OpenCDD’s six dictionaries, virtually every entity has registrant 0112.

Semantic

A short identifier for the conceptual area. For IEC CDD content this is almost always 2 (electrotechnical / information structures).

Scheme

Identifies the dictionary. The hyphen in the IEC publication number is replaced with an underscore (IEC 61360-4 → 61360_4). Examples:

Per IEC 61360-1 §5.2: “The hyphen ‘-’ in ‘61360-4’ is replaced by an underscore ‘_’.” — this is a hard rule of the IRDI scheme.

Code

The human-readable identifier inside the dictionary. Codes are:

• 3 letters + 3 digits for content entities (AAA021, AAD009).
• MDC_ prefix for meta-class and meta-property codes (MDC_C002, MDC_P004) — these are part of the dictionary schema, not domain content.
• EXT_ prefix for extensions outside the IEC core (e.g. EXT_C001 for ViewControl).
• UNIVERSE for the virtual root class of a classification tree (per IEC 61360-1 §21.1).

Codes are unique within a scheme but not globally unique — always pair a code with its scheme (or use the full IRDI) when communicating across dictionaries.

Short form

When context is unambiguous, IRDIs appear in a short form that is just the code (AAD009). The OpenCDD browser uses short form in the class-tree sidebar, breadcrumbs, and table cells, and the full IRDI in the entity hero, raw-properties dump, and copy-to-clipboard button.

The short form is what IEC 61360-2 calls the code attribute; the full form is the irdi attribute.

Special IRDI families

Meta-class IRDIs (MDC_C###)

These identify the seven meta-classes of the dictionary schema itself. They are not content entities — they describe what kind of entity something is.

Every entity in a CDD dictionary has a meta_class_irdi attribute pointing at one of these. The browser uses it to decide which badge colour to render and which subtype-specific methods are available.

Meta-property IRDIs (MDC_P###)

These identify the standard attributes that any entity can carry — preferred_name (MDC_P004), definition (MDC_P006), superclass (MDC_P010), is_case_of (MDC_P013), and so on. There are roughly 100 of these in the IEC 61360-2 EXPRESS schema.

You will see them most often in the raw_properties payload, where they appear as hash keys (MDC_P004.en, MDC_P006.de, MDC_P010, etc.).

Workbook-column codes (C###)

The IEC .xls export format includes additional columns that have no MDC_P### equivalent — publisher, status level, responsible committee, change-request ID. These appear in raw_properties with C### codes (C011 for publisher, C016 for status level, C002 for change-request ID, etc.). The browser’s typed view surfaces them as named fields (e.g. status_level, publisher); the raw view keeps the original codes.

IRDI vs ICID

ISO 13584 / IEC 62656-1 also defines the International Concept Identifier (ICID), a URL-friendly IRDI variant used in the ParcelMaker spreadsheet format. It looks like:

0112-2---61360_4%23AAD009

The ICID replaces / with -, drops /// to ---, and percent-encoded # as %23. ICIDs appear in _page.html URLs on cdd.iec.ch and in some legacy export formats. The OpenCDD browser normalises both forms to canonical IRDIs internally.

Parsing IRDIs in code

TypeScript

interface IRDI {
  registrant: string | null;
  semantic: string | null;
  scheme: string | null;
  code: string;
  version: string | null;
}

function parseIRDI(input: string): IRDI | null {
  const s = input.trim();
  if (!s) return null;

  // Full form: registrant/semantic///scheme#code
  const full = s.match(
    /^(?<r>[^/#\s]+)\/(?<s>[^/#\s]*)\/\/\/(?<sc>[^/#\s]+)#(?<c>[^#\s]+)(?:##(?<v>\d+))?$/,
  );
  if (full) {
    const g = full.groups!;
    return {
      registrant: g.r, semantic: g.s, scheme: g.sc,
      code: g.c, version: g.v ?? null,
    };
  }

  // Short form: just a code
  if (/^[^#/\s]+$/.test(s)) {
    return {
      registrant: null, semantic: null, scheme: null,
      code: s, version: null,
    };
  }
  return null;
}

Ruby

require "opencdd"

irdi = Opencdd::IRDI.parse("0112/2///61360_4#AAD009")
irdi.registrant  # => "0112"
irdi.semantic    # => "2"
irdi.scheme      # => "61360_4"
irdi.code        # => "AAD009"
irdi.short?      # => false

short = Opencdd::IRDI.parse("AAD009")
short.short?     # => true
short.code       # => "AAD009"

The Ruby IRDI.parse handles full, short, and ICID (-/%23) forms automatically and returns a frozen, comparable value object.

Citing IRDIs

When you reference a CDD entity outside the browser:

1. Cite the IRDI in full. 0112/2///61360_4#AAD009 is unambiguous; AAD009 alone is not.
2. Pin to a version when stability matters. Add (version 002, revision 05) after the IRDI so future readers know which definition you were working against.
3. Link to the OpenCDD page when a clickable reference helps. The URL is https://opencdd.github.io/d/{dict}/{type}/{code}/.
4. Do not invent new IRDIs. Only IEC TC 3 can mint IEC 61360 IRDIs. For private extensions, use the CDDP package format (planned) or your own registrant prefix.

Common pitfalls

• Hyphen vs underscore in scheme. IEC 61360-4 becomes 61360_4, not 61360-4. The IRDI grammar does not allow hyphens in the scheme position.
• Case sensitivity. Codes are uppercase. The IRDI grammar treats codes as case-sensitive; aad009 will not resolve.
• Letter O and I are forbidden in codes (to avoid confusion with 0 and 1). Codes use A–Z (minus O, I) plus 0–9.
• Leading zeros are significant. AAD009 and AAD09 are different codes.
• Version is not in the IRDI. An IRDI refers to the entity across all its versions. To pin a version, store the version/revision alongside the IRDI in your data.

Read more

• The CDD data model — how IRDIs fit into the larger entity model.
• Query cookbook — recipes for working with IRDIs in code.
• ISO/IEC 11179-6 for the normative IRDI definition.
• IEC 61360-1:2017 §5 for the dictionary identification attributes. section: “Concepts”