| "symbolic processing" means computing with symbols, not numbers. Like: (simplify '(2 * a + 4 * a)) -> (6 * a). An application for symbolic processing could be a rule-based system. The application then consists of a lot of rules and facts. Facts also could be symbols, not just numbers. Like a physical pressure value could be a number, but it could also be a qualitative value like low-pressure. A relatively old application (originating in the mid 80s) is real-time control with a rule-based system in technical systems. Technical systems could be a fleet of satellites, a chemical plant, a cement production plant, ... The software might get sensor inputs and based on rules may cause physical actions like opening or closing a valve, while getting more live sensor inputs, then possibly triggering other rules. Typically Lisp systems have some kind of GC and most of the time this will not allow real-time applications. There are are some specialized Lisp systems which have no GC and the application code is written in a way to not dynamically allocate memory during runtime - one says that the style is non-consing, where CONS is the basic operation to allocate a new list cell. This way they avoid garbage collections. This allows some real-time applications, like the mentioned rule-based process control software. This is rare and exotic stuff. It's also considered 'old AI' technology. The paper describes also something exotic: a concurrent Garbage Collector for a Japanese Lisp Machine, which runs a Lisp operating system - that was a thing when Japan was investing a lot into Artificial Intelligence in the 'Fifth Generation Project'. Such a GC would be useful so that the machine's network stack could be written directly in Lisp, but also for applications (similar to above control of external physical systems): robots, machines, production plants, ... It was thought that an important application domain for expert systems could be in industrial control systems. |