Clustering algorithms aim at modeling fuzzy (i.e., ambiguous) unlabeled pat
terns efficiently. Our goal is to propose a theoretical framework where the
expressive power of clustering systems can be compared on the basis of a m
eaningful set of common functional features. Part I of this paper reviews t
he following issues related to clustering approaches found in the literatur
e: relative (probabilistic) and absolute (possibilistic) fuzzy membership f
unctions and their relationships to the Bayes rule, batch and on-line learn
ing, prototype editing schemes, growing and pruning networks, modular netwo
rk architectures, topologically perfect mapping, ecological nets and neuro-
fuzziness. From this discussion an equivalence between the concepts of fuzz
y clustering and soft competitive learning in clustering algorithms is prop
osed as a unifying framework in the comparison of clustering systems. Moreo
ver, a set of functional attributes is selected for use as dictionary entri
es in the comparison of clustering algorithms, which is the subject of Part
II of this paper [1].