Like the Roman god Janus (and many a politician), every web application has two faces: Its human face interacts with people, while its machine face interacts with computer systems, often as a result of those human interactions. Showing too much of either face to the wrong audience creates opportunity for error.
When a user interface—intended for human consumption—reflects too much of a system’s internals in its design and language, it’s likely to confuse the people who use it. But at the same time, if data doesn’t conform to a specific structure, it’s likely to confuse the machines that need to use it—so we can’t ignore system requirements, either.
