HOPP

Half Object Plus Protocol was published in volume 1 of Pattern Languages Of Program Design by Gerard Meszaros. Its Synopsis is:

Divide an object which needs to be accessed from more than one address space into two interdependent half-objects (one in each address space) with a protocol between them. In each address space, implement whatever functionality is required to interact efficiently with the other objects in that address space. (This may result in duplicated functionality, i.e., implemented in both address spaces.) Define the protocol between the two half-objects so that it co-ordinates the activities of the two half-objects and carries the essential information that needs to be passed between the address spaces.