[1] We use the term E-R model to represent the structural component of an object model.

[2] Consistent with the Smalltalk notation, receiver denotes the object to which a message is sent.

[3] The receiver of these messages may be any descendent class of PermanentObject

[4] brother is used if the same entity in the same role is used in multiple entity sequences, e.g., a query that joined Employee with PayCheck on Payroll, with TaxState on PayrollTax and with Department on Reports would use brother in the Pay Check JoinClass instance to connect to the TaxState JoinClass instance and in the TaxState JoinClass instance to connect to the Department JoinClass instance (each would have the Employee JoinClass instance as their prior and nil as their next).