How the registry works
The ACT-ID.io registry is built around a small set of clear principles. Understanding these principles makes the system easier to use and reason about.
Activities are the core unit
The registry is built around activities — the things being financed. An activity is a defined, describable economic action: generating electricity from offshore wind, renovating a residential building, operating an electric passenger rail service.
Each activity gets a unique, stable identifier in the
ACT-A-XXXXXX family. This identifier does not change.
If an activity definition needs to be updated materially, a new version
record is created and the lineage is tracked.
Activities are defined at a level of specificity that makes them useful for bond market purposes — not so broad that they are meaningless, and not so narrow that they become unusable across issuers.
Criteria are separate from activities
Eligibility criteria — the thresholds, conditions, and requirements that an activity must meet to qualify under a given framework — are tracked separately from the activity itself.
This separation matters because the same activity can be subject to different criteria under different frameworks, and criteria can change over time while the activity stays the same.
Each criterion gets its own identifier in the ACT-C-XXXXXX
family and can be cited and versioned independently. A criterion always
references the activity or activities it applies to.
Mappings are first-class objects
The relationship between an Act ID activity and an entry in an external framework — the EU Taxonomy, ICMA Green Bond Principles categories, a national taxonomy, a sector classification — is not assumed or implied. It is an explicit, citable record.
Each mapping gets its own identifier in the ACT-M-XXXXXX family.
Mappings specify the type of relationship (exact, broader, narrower, or related)
and can be cited and updated independently.
This means that if a framework changes — or a new framework is published — the mapping can be updated without changing the underlying activity or criterion.
Provenance matters everywhere
Every record in the registry — whether an activity, criterion, or mapping — is supported by citations that show where the definition came from.
Citations reference the specific source: the regulation, the framework document, the technical annex, the section number. This makes the registry auditable and lets users trace every record back to its authoritative source.
Citations get their own identifiers in the ACT-R-XXXXXX family
and can be shared across multiple records.
Identifiers are hash-derived
Act IDs are not sequential numbers. They are derived from a hash of the record's content at the time of creation. This makes the identifier intrinsically tied to the record — a different hash means a different record.
Hash-derived identifiers also make the system more resilient: the identifier cannot be accidentally reused, and two identical records in different contexts will naturally produce the same identifier.
The six-character alphanumeric suffix (e.g. 7K4M2Q) is derived
from the first six characters of a truncated SHA-256 hash of the record content,
encoded in a URL-safe base-36 format.
Version history and lineage
When a record needs to be updated materially, the original record is retained
and a new version is created. Lineage records (ACT-L-XXXXXX)
track the relationship between versions.
This means that users who have cited an older version of a record can see exactly how the definition has changed — and decide whether to update their own references.
Assignments (ACT-S-XXXXXX) track where an Act ID has been
used — for example, in a bond framework or SPO opinion — as a record of
adoption.
Object types in the registry
The core unit. A defined financed activity.
Eligibility thresholds and conditions, tracked separately.
Relationships to external frameworks, taxonomies, and classifications.
Provenance records citing the source of a definition.
Records of where an Act ID has been used.
Version history tracking changes over time.
Questions about the methodology?
We welcome feedback from market participants on the methodology. Get in touch.
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