One approach was based on what’s called “expert systems.” Especially popular in the late 1970s and 1980s, this involved the collection of large amounts of facts and the creation of rules that computers could apply in chains of logical reasoning to make decisions. As one technologist has noted, this rule-based approach couldn’t scale to match the complexity of real-world problems. “In complex domains, the number of rules can be enormous, and as new facts are added by hand, keeping track of exceptions to and interactions with other rules becomes impractical.”5
