NewDatabase creates a Clients'Database instance.

ErrAssignToGroup indicates failure to assign member to a group.

ErrFailedToRetrieveAll failed to retrieve groups.

ErrFailedToRetrieveChildren failed to retrieve groups.

ErrFailedToRetrieveMembers failed to retrieve group members.

ErrFailedToRetrieveMembership failed to retrieve memberships.

ErrFailedToRetrieveParents failed to retrieve groups.

ErrGroupNotEmpty indicates group is not empty, can't be deleted.

ErrMemberAlreadyAssigned indicates that members is already assigned.

ErrMissingParent indicates that parent can't be found.

ErrUnassignFromGroup indicates failure to unassign member from a group.

Database provides a database interface.