Schematic diagram of BioProject hierarchies. A) Large initiatives that have distinct sub-projects may have more than one level of umbrella project. For example, a top-level umbrella project groups all components of the initiative; mid-level umbrella projects reflect distinct branches of the project (such as sequencing vs. epigenetics); and several submission projects denote distinct project data types (e.g., genome sequencing, transcriptome, epigenetics, etc.). B) Other initiatives may be organized under a single umbrella project with one or many submitted projects that are connected to data. Note that a given submission project may have no connection to any hierarchical umbrella projects, or may be connected to more than one organizational layer, and there may be connections directly between submitted projects such as the indicated RefSeq to GenBank link.