Entity relationship model of the Ensembl schema. Tables are represented as divided rectangles consisting of a boldface table name at the top and a list of table attributes and attribute types below. Internal identifiers and join tables are omitted. Relationships between tables are represented by lines labeled with the relationship type: 1___1...n one to one-or-many relationship; 1___1 one-to-one relationship; 1___0...n one to zero-or-many relationship; 1...n___1...n one-or-many to one-or-many relationship; 1...2___0...n one-or-two to zero-or-many relationship.