The program called Heuristic DENDRAL solves scientific induction

problems of the following type: given the mass spectrum of an

organic molecule, what is the most plausible hypothesis of organic

structure that will serve to explain the given empirical data. Its

problem solving power derives in large measure from the vast amount

of chemical knowledge employed in controlling search and making

evaluations.

A brief description of the task environment and the program is given

in Part I. Recent improvements in the design of the program and the

quality of its performance in the chemical task environment are

noted.

The acquisition of task-specific knowledge from chemist-'experts',

the representation of this knowledge in a form best suited to

facilitate the problem solving, and the most effective deployment of

this body of knowledge in restricting search and making selections

have been major foci of our research. Part II discusses the

techniques used and problems encountered in eliciting mass spectral

theory from a cooperative chemist. A sample 'scenario' of a session

with a chemist is exhibited. Part III discusses more general issues

of the representation of the chemical knowledge and the design of

processes that utilize it effectively. The initial, rather straight-

forward, implementations were found to have serious defects. These

are discussed. Part IV is concerned with our presently-conceived

solutions to some of these problems, particularly the rigidity of

processes and knowledge-structures.