This repository provides a set of large OWL files that are useful for testing software. The files themselves are not distributed as they are too large! Rather this is a set of makefiles that download or generate them. To run you will need robot (http://robot.obolibrary.org/) and horned-owl (https://github.com/phillord/horned-owl) installed. Robot is in Java and requires quite a bit of memory to use. Horned is written in Rust and is much more efficient, but is not feature complete with Robot (in fact, big-owl was created partly to test horned!). However, Horned is rather more aggressive with it's resource use. If you don't have enough, it may crash your machine. The directories contain: dto:: The Drug Target Ontology isn't particularly large, but has lots of imports. go:: The Gene Ontology. Large, and in both normal and "plus" forms many-classes:: Generated ontology with various numbers of class declarations and nothing else ncbitaxon:: Very large and real ontology