Incremental Computation: What Is the Essence?

Incremental computation aims to compute more efficiently on changed input by reusing previously computed results. We give a high-level overview of works on incremental computation, and highlight the essence underlying all of them, which we call incrementalization – the discrete counterpart of differentiation in calculus. We present the gist of a systematic method for incrementalization, and a systematic method centered around it – called Iterate-Incrementalize-Implement – for program design and optimization, as well as algorithm design and optimization. We illustrate the methods with example applications in arithmetic computations, recursive functions, graph analysis, and distributed algorithms. At a meta-level, with historical contexts and for future directions, we stress the power of high-level data, control, and module abstractions in developing new and better algorithms and programs as well as their precise complexities.