Understanding bots through 4 interface categories

"A rose by any other name would smell as sweet," to paraphrase a famous bard. There is a huge ongoing boom in messaging-based applications coming to market, generically called "bots." Regular readers of technology sections are no doubt also aware that, by most accounts, the performance and adoption of these bots has failed to match the hype. Is the technology premature, are businesses rushing in too quickly, or are bots inherently limited? The first step to answering that question is deciding what "bot" even means.