A Comparative Study of Open-Source Fuzzy Modelling Toolkit Licenses and Features

The practice of distributing software as open-source, which serves as a pillar for Open Science, can benefit future research in the field of fuzzy logic by enabling access and increasing the maintainability of free fuzzy logic frameworks alternatives to closed commercial solutions. Most open-source software uses a distribution license, with a wide range of restrictions and requirements on the distributions of these tools and their derived works. Therefore, understanding each license limitation and requirement is essential to ensure an ethical research process and avoid legal issues from breaching the open-source license. However, there is a lack of comparative research on the current state of open-source licenses for fuzzy modelling toolkits and frameworks. Previous studies are outdated or incomplete, missing some of the most popular open-source fuzzy frameworks or a detailed analysis of the licenses used. Our research analysed 20 of the most prominent open-source toolkits and categorised them based on their licenses, with qualitative comparisons of their characteristics and limitations. In our study, we note a concerning scenario where a potential license violation may impede the publication and dissemination of academic works derived from fuzzy toolkits using the GPL license. Additionally, we identify a gap in open-source fuzzy toolkits with support for Fuzzy Control Language (FCL) and Type-2 fuzzy sets. Finally, this study aims to support and guide future researchers in selecting the fuzzy toolkit that best matches their research problem without infringing the open-source licenses used, with an intuitive and up-to-date overview of the licenses and features of open-source fuzzy modelling frameworks available.