KEGG (Kyoto Encyclopedia of Genes and Genomes) database is a database used for systematic analysis of metabolic pathways and functions of gene products in cells. KEGG helps to study genes and its expression information as a whole network. KEGG integrates data from genomes, chemical molecules, and biochemical systems, including metabolic pathways (PATHWAY), drugs (DRUG), diseases (DISEASE), gene sequences (GENES), and genomes (GENOME).