Building a Knowledge Base

From early experience building the DENDRAL system, it was obvious to us that putting domain-specific knowledge into a program was a bottleneck in building knowledge-based systems (Buchanan et al., 1970). In other systems of" the 1960s and early 1970s, items of knowledge were cast as LISP functions. For example, in the earliest version of DENDRAL the fact that the atomic weight of carbon is 12 was built into a function, called WEIGHT, which returned 12 when called with the argument C. The function "knew about" several common chemical elements, but when new elements or new isotopes were encountered, the function had to be changed. Because we wanted to keep our programs "lean" to run in 64K of working memory, we gave our programs only as much knowledge as we thought they would have to know. Thus we often encountered missing items in running new test cases. It was very quickly seen that LISP property lists (data structures) were a superior alternative to LISP code as a way of storing ...