Planning problems are non-deterministic in nature because they involve many considerations and interacting factors. The complexity of the problem is the real challenge. This work implements an inference mechanism within a constraint network by deducing plans through the relationships between objects. The relationships between objects model the links between structural and behaviural properties of the planning entities. This paper explains the uses of constraint knowledge which is incorporated into objects and how to propagate such constraints over the network of objects. This paper also elaborates how the combination of the deductive process and abductive knowledge works together.