(1) what The DOM response service, as I understand it, is an icetray service which can transform a series of PDF values describing the expected distribution of PE times (for some given track hypothesis and a given DOM) into a corresponding expected ATWD or FADC waveform. In a sense it's the inverse of a feature extractor, but not exactly. An important difference with a DOMsimulator is that it takes a PDF for input instead of a series of SPE hits. (2) why We need a response service for the waveform-based likelihood reconstruction, because photonics and other PDFs only give a sort of Platonic Idea of the shadow trace which we measure in the DOM cave (sorry, Berkeley guys). The distribution of the photon hit times will be smeared by the PMT and suffer from saturation on all sorts of levels. And besides, the measured waveforms are not always long enough to hold the full signal. Therefore we should compare the measured signals not directly to the Platonic PDF. At least, not in EHE events, where many signals suffer from saturation and too short waveforms. For example, the WF-likelihood should not give a large penalty for WF bins with only a tenth the expected number of PE is registered, if that WF bin is at its saturation value. In short, by using the DOM response service the WF-likelihood can do a so-called apples-to-apples comparison of hypothesis and measurement. (3) how The PDF-to-DOM-response transformation is made into a service so that it is separated from the WF calculation, both for the developers and for users.