Comment 4 for bug 861682

Both the Service and Role models use Integers for ID's & FK's:

    class Role(Base, KeystoneBase):
        id = Column(Integer, primary_key=True, autoincrement=True)
        service_id = Column(Integer, ForeignKey('services.id'))

    class Service(Base, KeystoneBase):
        id = Column(Integer, primary_key=True, autoincrement=True)

Source: https://github.com/openstack/keystone/blob/master/keystone/backends/sqlalchemy/models.py