The recent works on integration of large database systems distributed over wide-area networks concentrate on the adaptive and online techniques. Online property of data integration means continuous integration of transmitted data with the already available results. Adaptivity materializes in a form of dynamic adjustments to the data integration plans in a response to the recent characteristics of data transmission. Implementation of adaptive and online data integration needs the specialized systems of operations and transformations of integration plans. This paper describes a new class of elementary operations on increments and/or decrements of data and shows how to express data integration plans as sequences of elementary operations. We demonstrate that class of operations proposed in the paper is sufficient for implementation of online and adaptive data integration systems and we discuss the operational properties of such systems.