A method comprises predefining a reference data item; creating a relation and inserting a given data item of the set of data items into the relation; inserting each data item of the set of data items into the created relation using a traversal method, wherein the order comparing step comprises in case a comparison result of the currently traversed data item with the reference data item is different from a comparison result of the to be inserted data item with the reference data item inverting the decision logic, and using the inverted decision logic in the decision step; and providing the created relation.