The PDB is useful for scientists studying structural biology and structural genomics. Many scientists have to send their information to the database. Major scientific journals and some funding agencies, such as the National Institutes of Health in the United States have rules telling scientists to send the data to the PDB. The PDB has the original or primary data. Hundreds of other databases reuse the data. These secondary databases organize the information in different ways. For example, both SCOP and CATH put structures into groups organized by type of structure and ideas about how they are related through evolution. Gene ontology puts the data into groups based on genes.