A search for a document is based in part according to how the document fits into the eLibrary data structure. The eLibrary data structure has a hierarchical design that contains six "Libraries":
Within each Library, there are two categories of documents: Issuances and Submittals. Each Category is divided into classifications, which are then segmented by Type. Documents usually fall into one or more of the Libraries (on the basis of the FERC regulatory programs). Thus, the hierarchy is from top to bottom.