Book Reviews Netl: a System for Representing and Using Real-world Knowledge

This is a "slightly edited version" of Fahlman's 1977 Ph.D. dissertation. Fahlman presents a knowledge representat ion organized as "a pat tern of interconnect ions of very simple parallel processing elements: node units which can store a dozen or so distinct marker-bits, and link units which can propagate these markers from node to node, in parallel through the network" [p. 1]. Fahlman considers it to be important that "using these marker-bit movements, the parallel network system can perform searches and many common deductions very quickly: the time required is essentially constant , regardless of the size of the knowledge-base" [p. 1]. However , this timing result depends on the existence of parallel ne twork hardware. An appendix unconvincingly presents a design of such hardware, but the body of the book presents a knowledge representat ion structure which can be considered on its own merits, independently of such timing considerations.