1. A method comprising: generating a source model based on a source data structure and a source data structure format; generating a target model based on a stored target data structure and the target data structure format in a preceding synchronization or a resulting from updating specific synchronized data; obtaining a proposed model based on mapping a relationship between the source model and the target model; receiving, from a user, information specifying a change to the proposed model, wherein the information presenting the change to the proposed model includes an operation specifying at least one of inserting, deleting, or changing a relation or an attribute of objects of the proposed model; determining, by a computing processor, a conflict based on a comparison of the proposed model and the target model, wherein the determined conflict includes at least one of finding an object which has not been part of the target model in the preceding synchronization, or finding an object of the preceding synchronization which is no longer part of the proposed model, wherein the found object includes a relationship being part of the proposed model and the target model or an attribute having different values in the proposed model and the target model; presenting the determined conflict and solutions to resolve the determined conflict to the user via an graphical user interface, wherein the solutions are represented as a sequence of operations on the proposed model; selecting a solution of the solutions from the user to resolve the determined conflict; applying the selected solution to at least one of the target model or the proposed model to resolve the conflict; and storing an operation representing the change to the proposed model; and storing the proposed model after making the change as a new version or a second state in the target data structure.