What is a thesaurus, what is the difference to a taxonomy or an ontology?

Summarization: A thesaurus is expressive enough to improve most enterprise applications significantly, but it is not too complex to create and maintain it in a sustainable way. All three are types of controlled vocabularies, which contain terms with their synonyms and alternative spellings combined to form concepts. A taxonomy is the simplest variant as it contains only terms that are organized into a hierarchical structure. A thesaurus adds non-hierarchical relationships between concepts and other properties to each concept. Ontologies are on the heavy end of the spectrum. Ontologies can express axioms and restrictions. This maximum in expressivity has the drawback that ontologies are hard to create, maintain and handle. We believe thesauri hit the sweet spot between expressive semantics and ease of handling, and designed PoolParty to be a tool that makes creating and maintaining them straightforward.