The grammar of the house and of the city. Theoretical approaches for generating project

This contribution presents the conceptual premises and some methodological aspects of a general evaluation model to support the urban fabric redevelopment project of the historic city. The model, in its general directives, is tool superordinate to the project, which enables the functions of evaluation to generate a multiplicity of possible alternatives. The model is consistent with a representation of reality by objects and characteristics, starting from the identification of the minimum units of study, the “value bearers”, and their representation in the space of the project by means of a large number of terms of value; this information base is created by means of a multiplicity of formalized observations in a unitary lexicon and collected in an extensive database. The strong characterization the historic urban fabrics can be the reference of renovation policies, which, recognizing the significance of these forms, generate the arrangement of conservation and change – the rule and the exception. The theoretical core of this contribution is the relationship between urban forms and the three main gammars: constructive, selective and generative. A constructive grammar-based approach prescribes the elements to be used and the ways in which they must be put together, according to a typically object-oriented approach, based essentially on the constraint imposed in highly structured contexts that admit only minor variations with respect to the consolidated and recognized norm. A selective grammar lists the elements to be combined and the combinations to be avoided, allowing ample possibilities for reforming weakly structured contexts. No definitive form is ever supposed, coherently with a performance-based approach, since the elements are combined according to an overall logic that is part of the context with reference to its perspective, to values not yet present. A generative grammar is a system of rules the combination of which allows to produce a potentially unlimited repertoire of expressive forms coherent with these rules; consequently, these forms can be compared if they are consistent with present and future values. This grammar is consistent with an axiological approach referable to a system of values, rather than just rules, which implement a broad social and eco-systemic prospect.