Three Tier Classification of RS

Therefore, we categorise research software into three tiers based on scope, potential for reuse, and social dependencies following the model introduced by the Australian Research Data Commons (ARDC) [Australian Research Data Commons, 2022] and adopted by the EVERSE project (https://everse.software/RSQKit/three_tier_view, last access 2026-03-10), which is also closely related to the application classes used by the DLR [Schlauch et al., 2018]. However, we are adapting the naming of the three tiers for reasons detailed further below. This categorisation should not be understood as a hierarchy of quality, but rather as a pragmatic framework designed to facilitate communication and collaboration across institutions and research communities. The tiers are also not mutually exclusive, meaning that software can evolve from tier 1 to tier 2 to tier 3 over time, depending on its adoption and use within the research community.

Tier 1 refers to software that is developed primarily for personal use or an individual project, with limited external adoption and minimal dependencies by other researchers or projects.
Tier 2 includes software that is reused across multiple research initiatives, indicating growing community interest and reliance.
Tier 3 encompasses software that has become a shared resource relied upon by multiple institutions or disciplines. This software requires sustained investment, governance, and community stewardship.

Based on these descriptions, we propose the following terms for these tiers:

Tier 1 - Personal or Project Software
Tier 2 - Community or Shared Software
Tier 3 - Critical / Foundational Software

We have split up the description and the terms because we see a potential for confusion with the widely used term "infrastructure": The third tier is referred to as "research software infrastructure" by ARDC and EVERSE. The common understanding of tier 3 describes software with a central role in the ecosystem, with broad adoption, critical in multiple research areas, and such with high social dependencies. The emphasis is on the software artefact itself and its structural importance.