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C. FERREIRA In E. Lutton, J. A. Foster, J. Miller, C. Ryan, and A. G. B. Tettamanzi, eds., Proceedings of the 4th European Conference on Genetic Programming, Lecture Notes in Computer Science, Vol. 2278, pages 51-60, Springer-Verlag, Berlin, Germany, 2002.
Discovery of the Boolean Functions to the Best Density-Classification Rules Using Gene Expression Programming
Gene Expression Programming
 
The phenotype of GEP individuals consists of the same kind of diagram representations used by GP. However, these complex entities are encoded in simpler, linear structures of fixed length - the chromosomes. Thus, the main players in GEP are two entities: the chromosomes and the ramified structures or expression trees (ETs), being the latter the expression of the genetic information encoded in the former. The process of information decoding (from the chromosomes to the ETs) is called translation. And this translation implies obviously a kind of code and a set of rules. The genetic code is very simple: a one-to-one relationship between the symbols of the chromosome and the functions or terminals they represent. The rules are also very simple: they determine the spatial organization of the functions and terminals in the ETs and the type of interaction between sub-ETs in multigenic systems.

In GEP there are therefore two languages: the language of the genes and the language of ETs and, in this simple replicator/phenotype system, knowing the sequence or structure of one, is knowing the other. In nature, although the inference of the sequence of proteins given the sequence of genes and vice versa is possible, practically nothing is known about the rules that determine the three-dimensional structure of proteins. But in GEP, thanks to the simple rules that determine the structure of ETs and their interactions, it is possible to infer exactly the phenotype given the sequence of a gene, and vice versa. This bilingual and unequivocal system is called Karva language. The details of this language are given in the remainder of this section.
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