Zarr.NET licensing model

[glopesdev]

It is really great to see a project stepping in to implement Zarr in .NET. If successful, this would fill a very prominent gap in the adoption of Zarr for open-data science acquisition using .NET tools.

As the creator of open-source instrumentation tools, I was excited to see this project come to life. However, I was surprised about the GPL licensing choice for Zarr.NET, as it seems to break compatibility with all other published Zarr implementations:

• zarr-python (MIT)
• zarr-java (MIT)
• zarrs (MIT/Apache)
• cpp-zarr (BSD-3)
• zarr.js (Apache)
• Zarr.jl (MIT "Expat")
• pizzarr (MIT)
• zarr-ml (BSD-3)

I anticipate this will make it harder to adopt Zarr.NET in mixed code bases wanting to integrate data analysis tooling with acquisition and instrumentation tools in a variety of contexts.

Given both the Zarr ecosystem and .NET itself are permissively licensed, I was wondering what might be the motivations behind the current choice of license, and the expectations for broader adoption of Zarr.NET by the community going forward.

[BiologyTools]

Thank you for taking the time to look at the project.

You're right that many Zarr implementations use permissive licenses. The licensing choice for Zarr.NET was made deliberately and follows a model that already exists in the bioimaging ecosystem. For example, Bio-Formats — one of the most widely used interoperability layers in microscopy — is GPL licensed and has nonetheless been successfully integrated into both academic and commercial imaging platforms for many years.

Zarr.NET is being developed primarily to support OME-Zarr, the next-generation cloud-native bioimaging format from the Open Microscopy Environment community. The goal is to provide a robust native .NET implementation so that acquisition, visualization, and analysis tools built in the .NET ecosystem can fully participate in the OME-Zarr workflow.

Importantly, the license of a particular implementation does not affect interoperability. Zarr is a storage specification and file format, so datasets written by Zarr.NET remain fully compatible with other implementations such as Python, Java, C++, and JavaScript.

The GPL license helps ensure that improvements to the core implementation remain available to the community. At the same time, for organizations that need to integrate Zarr.NET into proprietary software without GPL obligations, commercial licensing options are available.

Some companies building microscopy acquisition and analysis tools in .NET have already expressed interest in this model, since it allows them to adopt OME-Zarr while still maintaining proprietary software stacks.

I appreciate the discussion — feedback like this is valuable as the .NET ecosystem around Zarr and OME-Zarr continues to grow.

[glopesdev]

Zarr.NET is being developed primarily to support OME-Zarr

Do you mean bioio-ome-zarr or ome/ome-zarr-py? Both of those projects seem to have permissive licenses, either under BSD-3 or a variation of MIT.

I'm not sure I understand your argumentation, but wish you luck for the project.