Style is the current commonly used term for a concept that has been known and used in Art History and Art Critique through the ages: canon for plastic and graphical arts, genera in architecture (as in the derivative French word genre, which is used in broader contexts), maniera, as used by Giorgio Vasari to describe individual styles of artists, nations and periods (as in the derivative English word manner). A style should identify the nature of an organic but simultaneously disseminated coherence. This is a difficult concept to be captured by a formal model.

Transformations in Design: A Formal Approach to Stylistic Change and Innovation in the Visual Arts by Terry Weissman Knight (1994) tries to develop "a formal model of transformations of languages of design" using shape grammars, a formalism introduced by G. Stiny in this paper (1972). Although the approach described here is really interesting, what I found most inspiring in the book is the first chapters, that provide an historical survey of some philosophical theories about style and stylistical change.
In particular, Knight maintains that:

The concept of style is used basically as an ordering principle. It allows the vast domain of individual artifacts and phenomena to be structured. [...]
Within the arts, the concept of style is typically used to describe consistencies among works that are products of an individual, school, culture, time period, or geographic region. Once stylistic categories are established, these are turned to predictive purposes, to identify works of unknown origins; [...]
The grouping of works of art into styles is a prerequisite for studying stylistic transformations.

The common assumption behind these theories is that aesthetic choices are ultimately driven by forces that lie outside the conscious free will of the artists and the craftsmen.

Of particular concern to the historian are the relationships between successive styles in time, which enable him or her to study change. Fundamental to the study of change is the assumption of some continuity of forms through time agaist which change can be measured.
This continuity is usually understood to be the results of the constraints placed on the artist by the tradition in which he or she works. Tradition provides the artist with a repository of forms and conventions which he or she may then vary to produce new forms and styles. Were it possible for the artist to trascend the tradition he or she inherits, and invent a completely new style from scratch, the results would be likely be unintelligible and uncommunicable.