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ADR-011: Data Model Conventions (ULID, Retention, Transfers)

  • Status: Accepted
  • Date: 2026-02-04

Context​

We need consistent identifiers across TypeScript, Go, and Rust, and clear retention policies for user data. We also need a transfer model that supports real-world equivalencies.

Decision​

  • Use ULID as the default identifier type across services.
  • Session retention:
    • Keep full session transcripts for 90 days, then anonymize.
    • Delete anonymous sessions older than 1 year.
    • "7-day TTL" applies only to cached artifacts (e.g., embeddings/index/summaries), not session retention.
  • Transfer model must support:
    • multi-course equivalencies (sets of source courses mapping to a target)
    • generic/elective credit targets (e.g., CPSC 1XX (3 credits))
    • credit conversion (source and target credits may differ)

Consequences​

  • All services must adopt ULID libraries compatible with their language.
  • Retention/anonymization jobs must be implemented and tested.
  • Transfer schema and resolution APIs must treat multi-course sets and generic targets as first-class.

Alternatives considered​

  • UUIDv4 everywhere: workable, but ULID provides better sorting semantics.
  • Model transfers as only 1:1 course mappings: insufficient.