Abstract: Information sharing is the basis of multi user collaboration in CSCW systems. First the requirements for the service of shared objects in CSCW is analysied. Then a collaboration supporting model of shared objects SOCSM/LSI is presented. The SOCSM/LSI uses the layered service interface to implement the cooperative functions such as access control, group awareness, and different presentation of shared objects. The SOCSM/LSI model can provide dynamic and flexible cooperative mechanisms for shared objects and can be applied to a quite wide range of CSCW applications.