Link between MachineInstr and MachineOperand

In the representation of the code after instruction selection (but before register allocation), in a MachineBasicBlock:
How/where is the result of a machine instruction linked to one of the machine operands of a subsequent machine instruction?
Asked differently: How/where are the links of the DAG implemented (specially between MachineInstr and MachineOperand)?

Frank

The missing information was that machine instructions employ a def/use semantic for their operands. The 'links' between input and output of instructions are the virtual registers, first 'defined' (as output) and in a subsequent consumer instruction 'used' (as input).

Frank