The molecular frameworks, also known as Murcko scaffolds, are defined as the part of the molecule that contains all ring systems and chains that link them, while all side chains are removed. Bemis and Murcko also described the graph framework obtained by disregarding atom and bond types, which later became known as the generic Murcko scaffold , as shown in Figure . The reason for abstracting the structure further is that changing atom and bond types results in a different scaffold, and thus compound class. Xu and Johnson explored how different levels of abstraction can create a hierarchical classification, where the leaves are the molecular frameworks, and the root, the most abstract molecular representation, is the reducedskeletal cyclic system (similar to the reduced generic scaffold shown in Figure ), where ring size information is disregarded and for which a molecular equivalence index (MEQI) descriptor was invented . On the other hand, Schuffenhauer et al. explored a different strategy for creating a hierarchy -the Scaffold Tree. The central idea is to sequentially remove parts of the Murcko scaffold based on predefined rules and group compounds together at the different levels of the tree. Additionally, more abstract representations of the Murcko scaffold for nonhierarchical grouping of structures have also been developed. For example, the analysis of DNA- encoded libraries (DELs), where the information at which position the DNA tag is attached to a molecule is important, the reduced complexity molecular framework (RCMF) descriptor has been introduced . Rings are grouped into predefined ring classes, chain linkers are described by their length, omitting atom type information, and the connectivity between rings is described by the topological angle at which they are linked.