# OME-Zarr RFC-9 sync meeting

Goal: Revise RFC-9 and prepare it for review

Wednesday, August 27th 2025, 3pm CEST / 9am EST
https://uu-se.zoom.us/j/68310667741

## Participants

- [ ] Josh Moore (editor; technical input welcome)
- [x] Jonas Windhager (author)
- [x] Dominik Kutra (co-author)
- [x] Mark Kittisopikul (co-author)
- [x] Norman Rzepka (co-author)

## Preparation

Please comment - ideally prior to the call - if anything is missing/unclear/wrong:

https://docs.google.com/document/d/14CHijFiqxKmpO6aDcQGJb6WPnyLVxYucnE2CzZ6cNBM/edit?usp=sharing

## Agenda

- Very (!) brief recap of the RFC's background/motivation/goals (Jonas) - [slides](https://docs.google.com/presentation/d/1mHsoZuGOvM4NdJEdVE_Er6nv1ZRvHvmVBD9gFqOb0Pk/edit?usp=sharing)
- Discussion of the open questions, based on document above:
- Content specification
- Storage backend specification
- Entrypoint specification
- File extension specification
- Planning
- Define co-authors
- List necessary changes to the current RFC
- Distribute tasks (if desired/necessary)
- Estimate timeline

## Minutes

Scope:
- "this is how to store OME-Zarr in a ZIP file" (as opposed to: "this is how to store OME-Zarr in a single file")
- not a "profile" (avoid scope creep!)

Content: do not specify (out of scope, leave this up to the tools)

Storage backend: ZIP, recommendations as suggested, perhaps use comment field to indicate "optimally" packaged zip following those recommendations

Disallow ZIP recursion *for now*; next steps could be:
- ZIPs in collections (see collections spec)
- ZIPs in (directory-backed) OME-Zarrs
- Nested ZIPs

Entry point: zarr.json in root, recommended as first central directory record and first file (see storage backend recommendations)

File extension: specify custom extension (zarrx, zar, zx, ozp, ...?)
- reduces risk to "accidentally" create unoptimized zipped OME-Zarr (e.g. using onboard tooling)
- reduces risk to "accidentally" unpack a zipped OME-Zarr without first creating a directory (e.g. using onboard tooling)

Jonas revises draft, Dominik/Mark/Norman as co-authors providing feedback