The KEGG BRITE database is a collection of BRITE hierarchy files, called htext (hierarchical text) files, with additional files for binary relations. The htext file is manually created with in-house software called KegHierEditor. The htext file contains "A", "B", "C", etc. at the first column to indicate the hierarchy level. Each BRITE hierarchy file represents a classification system of KEGG objects identified by the KEGG Identifiers; for example, pathway-based gene classification or protein family classification by the K numbers, compound classification by C numbers, drug classification by D numbers, and disease classification by H numbers.

The binary relation files contain the relationship between KEGG objects and attributes, which can be dynamically added to the hierarchy file as additional columns using the join feature of the Brite hierarchy viewer. Many binary relation files are computationally generated from the KEGG database contents and shown in the left panel of the Brite hierarchy viewer.

The KEGG objects of BRITE files can be searched in the search box at the top of the KEGG BRITE page, in the search boxes of the Brite hierarchy viewer, and by the KEGG Mapper tools.

Each BRITE hierarchy file is identified by the combination of 2-4 letter code and 5 digit number (see KEGG Identifiers). The prefix has the following meaning:

• ko - Reference hierarchy (KO)
• org - Organism-specific hierarchy
• br - Non-KO hierarchy
• jp - Non-KO hierarchy in Japanese

Thus, the "ko" hierarchy file is manually created for the functional classifications of genes and proteins using the K numbers. Organism-specific hierarchy files are then computationally generated by converting K numbers to gene identifiers in each organism. The "br" hierarchy file is created for the functional classifications of chemical compounds, reactions, drugs, diseases, organisms, etc. using the KEGG identifiers other than the K numbers.