Chemical space occasionally referred to in the literature as the "chemical universe" is a concept that has become significant in chemoinformatics as an independent theoretical discipline . Chemical space refers to all possible molecules and multi-dimensional conceptual spaces representing their structural and functional properties. In other words, chemical space is a contraction of the "chemical descriptor vector space" defined by the numerical vector D encoding molecular structure and/or property aspects as elements of the descriptor vector D. Therefore, and in contrast to cosmic space, chemical space is not a physical space and is not unique, because anyone is free to customize its vector space based on structural and functional properties. Indeed, structural and functional representation is arguably the most relevant feature in virtually all chemoinformatics or computational studies .