The marriage of logic and objects is a very wide-ranging problem, approached with various approaches, depending on the purpose. In this article, we are interested in the modelling of the state and the change of the state of an object in logic programming. After a state of the art on the subject, presenting the various aspects as well as different solutions proposed in the literature, the article then proposes a mechanism of versions of objects based on the mechanism of unification and on the use incomplete structures. Indeed, the overview of an incomplete structure can be used to allow the entry of new information by means of unification and thus to foresee the future. This mechanism makes it possible to construct the history of an object by unification and to undo it by backtracking. The changes of state are thus made and defeated, without effects of edge, in synchronization with the backtrack.