In OKF v0.2 (§5.1), the materials a concept derives from are recorded in a sources frontmatter list rather than a body # Citations heading. This keeps external provenance (where the knowledge came from) in structured frontmatter, distinct from internal cross-links (how concepts relate) in the body.

Changed from v0.1. v0.1 recommended a numbered # Citations heading at the bottom of a concept document. v0.2 supersedes that list with the sources frontmatter family (§13.1). Consumers SHOULD read sources and MAY still parse a legacy # Citations body list for v0.1 documents.

The sources list

sources:
  - id: ga4-schema
    resource: https://developers.google.com/analytics/bigquery/export-schema
    title: GA4 BigQuery Export schema
    author: team:ga4-docs
    usage_count: 5000
    last_modified: 2026-05-30
usage_window: { from: 2026-06-01, to: 2026-06-30 }

Each entry:

• resource — REQUIRED within an entry. Names either a concrete artifact a consumer can follow or a scope descriptor it cannot (e.g. all queries in BigQuery project X).
• id — Optional stable key used to attribute individual claims. SHOULD be present when the body cites the source.
• title — Optional human-readable label.
• Credibility signals (all optional): author (an actor, §7 — an authority signal), usage_count (how often resource was exercised over usage_window — an adoption/liveness signal), and last_modified (when the source itself last changed — a recency signal, distinct from generated.at).
• usage_window — Written once as a sibling of sources, it frames every usage_count with a { from, to } range; a single entry MAY override it.

OKF records objective per-source signals rather than a stored credibility score — a score is subjective, unportable, and goes stale. Credibility is inferred from the signals, the same way trust tiers are.

Where a source's resource may point

A sources[].resource accepts (§6.2):

1. an absolute URL to the external source;
2. a bundle-relative path to another concept; or
3. a path into a references/ subdirectory that mirrors external material as first-class OKF concepts.

That third option is the spec's blessing for keeping source material inside the bundle: PDFs, images, transcripts, .mov files, captured web pages. Store the asset under references/ and wrap it in a type: Reference concept that points at it — the source becomes a citable, linkable node in the graph rather than an external URL that may rot. Lineage is expressed through links, not a dedicated field: when a resource points at another OKF concept, the derivation edge already exists in the bundle graph (§6), so a consumer MAY recurse into that source's own sources and let credibility propagate.

Per-claim attribution: footnotes

To attribute a specific claim, use a markdown footnote whose label is a sources[].id:

The `events_` table is sharded daily as `events_YYYYMMDD`.[^ga4-schema]

[^ga4-schema]: GA4 BigQuery Export schema

The footnote label is the join key into sources; consumers resolve attribution through the matching entry, not by parsing the footnote prose. Labels are keyed rather than positional (sources[0]) because agents constantly rewrite these documents — a positional index misattributes silently the moment the list is reordered, whereas a stable id survives reordering.

Canonical source vs. derived text

A useful discipline: separate the canonical source from the derived text. A references/ concept holds a stable pointer to the original asset (via resource or an embedded/linked file) and carries extracted text, a summary, or a description — so the source is preserved for provenance while the derived text stays useful for retrieval (agents can read it without opening a binary). The practical rule: if a document is part of the knowledge base, keep a stable pointer to it in the bundle; if it is merely incidental supporting material, cite it externally and leave it out. This bundle applies the pattern in OKF vs. RAG infographic (images stored under assets/, wrapped in a Reference concept with descriptive alt text).

Citations

1. OKF Specification (SPEC.md)