Open Data

Last updated: 19 July 2026

Contains information from The Session, which is made available here under the Open Database License (ODbL).

1. Where the tunes come from

Sessionist's tune catalogue is built from the community-contributed tune database of theSession.org, published as open data dumps at github.com/adactio/TheSession-data. We are deeply grateful to theSession's contributors and maintainers — the catalogue exists because that community shares its work openly.

2. The licence our catalogue carries

Sessionist's tune catalogue is a derivative database of theSession data and is itself made available under the Open Database License (ODbL) 1.0. We add no restrictions of our own to that data. The ODbL covers the tune database only: Sessionist's original content (guide audio, chord accompaniments, tune images, curated playlists) and the Sessionist app itself are separate works and are not part of the ODbL-licensed database.

If you want the tune data itself, the best source is the original: theSession publishes complete, current, machine-readable dumps at github.com/adactio/TheSession-data, and this page describes everything Sessionist's catalogue alters or adds (see below), as provided for by ODbL §4.6(b).

3. How our catalogue is derived (the alterations)

Sessionist's catalogue is produced from the theSession dumps by a deterministic conversion pipeline. In full, the alterations are:

• Selection and identity. Each tune setting (a specific version of a tune, in ABC notation) is carried through keyed by its theSession tune ID. Each setting is assigned a Sessionist version identifier derived from its source identity, so settings remain traceable to their theSession originals.
• ABC notation carried through. The setting's ABC notation is retained in the catalogue essentially as published; conversion to playable form (MIDI) happens inside the app at runtime.
• Title normalisation. A trailing article is folded for sorting ("The Maid Behind the Bar" sorts under M), with the presentation form retained separately.
• Classification fields parsed from the ABC headers — rhythm/tune type, meter, key root and mode — stored as enumerated fields.
• Computed playability fields, calculated from each setting's ABC note content: the set of pitch classes the setting contains, and its lowest and highest notes (as MIDI note numbers). These let the app match tunes to an instrument's range.
• Sessionist-added metadata. Genre tags, curation and lifecycle flags, editorial ratings, archive flags, and submitter credits carried from the source. Where these are merged into the catalogue they are part of the derivative database and covered by the same ODbL licence.
• Restructuring for delivery. Records are regrouped into a tune-keyed index with per-setting sub-records; fields identical across a tune's settings are de-duplicated against the parent record; JSON keys are shortened to compact codes; content hashes are computed for change detection. The result is published as JSON (a catalogue index plus per-setting files) for the app to download.

The pipeline is deterministic — the same dump in gives the same catalogue out — and is re-run against theSession's published updates.

4. Concerns

If you have any concerns about Sessionist's use of theSession data, email niall@sessionist.ie.