The purpose of tnis paper is to describe a recent effort to generate, classify, and enulerate the sttreoisomers of all organic chemical structures consistent with a given empirical formula. The resulting theory is then converted into an algorithm which is programmed for a computer. The resulting program is used as an aid for computer assisted structure elucidation [1]. The proper group theoretical formulation is the key to the solution of the problem and will be discussed here. Simply st,'..ed, the problem is to generate, classify, and enumerate the possible stereoisomers for an organic chemical structure of defined constitution.

A typical problem in dynamic stereochemistry is to determine the mechanism of the rearrangement of a chemical structure such as 1. (I 352) Many of the problems already studied have involved degenerate rearrangements (those which interconvert chemical structures of the same geometry apart from any difference in the ligands) and only these will be considered here. Two groups and the mapping (homomorphism) between them are crucial to the proper description of problems of this kind. The first of these is the symmetry group of the chemical structure's skeleton (i.e, without ligands) and is designated P. This may be a point group, the rotation subgroup of a point group, or a nonrigid symmetry group [1]. Generally, this group can be represented as a permutation group on the ligands or on the skeletal sites however, in the most general case, this group is best represented as a permutation-inversion group [1].

In collaboration with other members of the MOLGEN project, the author developed a representation system called the "Unit Package" which became operational in July 1977. In some cases (and usually in ignorance), this work has duplicated other representation work that was happening at about the same time. The Unit Package is now being used by several other projects including two away from Stanford. It is written in INTERLISP and runs under the TENEX and TOPS20 operating systems. It is an interactive system for building knowledge-based programs. It also provides a substantial virtual memory so that knowledge bases of several thousand nodes can created without sacrificing the IlTrERLISP environment.

This paper is a "final report" on the first version of the CRYSALIS project. As such, we will summarize the current state of the system and show where we plan to go with it. We have found that a design (in the software eng ineer ing sense) is a valuable tool for the evaluation and augmentation of a program, even when the design is done ex post facto. Using such a design, we discuss the major flaws of the existing system and how to correct them. Finally, we show how the architecture of this system could be useful for certain other task domains.

Counterexamples are provided disproving two independent claims that a simple but accurate method had been found to compute classes of symmetrically equivalent atoms in a molecule. Both methods are good approximations, but are nontheless ad hoc techniques which can sometimes fail to discriminate between atoms which arc, in fact, symmetrically distinct. A recem issue of this journal carried two papers23 dealing loop, at each stage of which a new score is computed for each directly or indirectly with "inexpensive" (in the sense of low atom based upon some function of the current score of that computational effort) methods of perceiving molecular atom arid the current scores of its immediate neighbors. More precisely, each article gives a set of rules term "score" here is used rather loosely; in the case of for scoring2 or comparing3 atoms in a molecule with the claim Morgan's algorithm it is an integer while in that of Shelley that if the scores are equal, or if the comparison shows no and Munk's it is a five-element vector. The important point difference, then the atoms arc symmetrically equivalent (i.e., is that a score is an entity which is associated with an atom can be interchanged by some symmetr) operation on the and which can be compared with the scores of other atoms molecule). Though both methods are doubtless very good in such a way that a strict "greater-less-equal" relationship approximations in the sense that they almost always yield the can be defined.

This is traditionally done with tne aid of a computer programmer acting as intermediary. The dire_t transfer of knowledge from an expert to the system requires a natural-language processor capable of handling a substantial subset of English. The development of such a natural-language processor is a long-term goal of automating knowledge acquisition; faciliting the interface between the expert and the system is a first step toward this goal. This paper describes BAUBAb, a program designed and implemented for hYCIN (Shortliffe 1974), a medical consultation system for infectious disease diagnosis and therapy selection. EAUdAb is concerned with the problem of parsing - recognizing natural language sentences aad encoding tnem into MICIN's internal representation. For this purpose, it uses a semantic grammar in whicft tne non-terminal symools denote semantic categories (e.g., infections and symptoms), or conceptual categories wnicn are common tools of knowledge representation in artificial intelligence (e.g.

An algorithm and its implementation as a computer program is described which for the first time permits the enumeration and construction of all the distinct stereoisomers possible which are consistent with a given empirical formula. The algorithm finds the stereocenters in a chemical structure, takes full account of any symmetry and produces the stereoisomers with cis/trans and R/C designations along with a canonical (unique) name. Examples of its use and a discussion of potential applications are given.

For This paper and the following one' describe the current effort most applications the familiar geometric point group is chosen to provide the CONG EN (for constrained structure generation) .22 In some spectroscopic applications It is necessary to take program with stereochemical capabilities.* This paper is primarily internal motion into account and specify a nonrigid symmetry concerned with the chemical and mathematical theory group.2b For applications in dynamic stereochemistry it is necessary to this effort. The following paper is concerned primarily necessary to consider the group of all permutations of identical with novel algorithms and the computer implementation.7 atoms and often several subgroups.3 Symmetry groups that A third paper considers the theory in greater mathematical include the point group and operations that invert chiral centers detail with some extensions to other topics.' are useful both in constructing chirality functions4 and in specifying the pseudochirality of a structure.5

We view this process as occurring in several stages, which together form a data hierarchy (Figure 3.1). The hierarchy offers an overview of DSS function and suggests a task partitioning suitable for a contract net approach.

The term "distributed database" encompasses systems of great diversity. The fact that there is a great variety of distributed databases makes their study and comparison difficult. It is hence important to clearly define what is meant by a given distributed database; it is also important to understand the spectrum of available alternatives. This understanding should elucidate the design of distributed databases and clarify the comparison of different systems. We will define a distributed database in a general way, so as to Include most types of distributed databases: A distributed database is a system that allows integrated access to a collection of logically independent databases [Garcia77].