I. Introduction
Machine learning (ML) provides efficient solutions for a number of problems that were difficult to solve with traditional computing techniques; e.g., object detection and language translation. ML cloud APIs allow programmers to incorporate these learning solutions into software systems without designing and training the learning model themselves [1], and hence put these powerful techniques into the hands of non-experts. Indeed, there are more than 35,000 open-source projects on GitHub that use Google or Amazon ML Cloud APIs to solve a wide variety of problems, among which more than 14,000 were created within the last 12 months.