Stephanie Balzer Thomas R. Gross Patrick Eugster A Relational Model of Object Collaborations and Its Use in Reasoning About Relationships. 323-346 2007 conf/ecoop/2007 ECOOP http://dx.doi.org/10.1007/978-3-540-73589-2_16 db/conf/ecoop/ecoop2007.html#BalzerGE07