Descriptive Conventions for Shape Grammars

Abstract

This paper introduces a new set of descriptive conventions for shape grammars, and illustrates howthey can be used to address problems with user experience. The shape grammar formalism has beenshown to be capable of generating designs such as Palladian villas, Prairie houses and Queen Annehouses. The formalism can describe the process to develop a design through the use of rules, symbols,and lines.The user’s experience in applying the rules is often neglected in the design of the grammars. Thiscreates four problems: 1) the user is unaware of the implicit sequencing of rules, 2) the user cangenerate invalid design states, 3) the user is forced to apply technical rules that do not change theoverall design, and 4) the user is only given a restricted set of design choices.To address these problems, a new set of descriptive conventions has been developed that provides alayer of abstraction built on top of the formalism. These conventions are currently being implementedusing the Visual LISP programming environment in AutoCAD. The program applies rules, whichincorporate the use of the new conventions, to produce a design.The conventions are based on two techniques. The first technique is an explicit control mechanism thatdetermines the sequencing of rules based on the success or failure of a rule application. Becausesome design changes require more than one rule, this allows the grammar to chain a sequence of rulesto create macros since. The second technique is a mechanism that demarcates an area of the drawingfor query. With this technique, a rule is able to recognize void spaces in a drawing.A comparison of the rules to construct a bi-laterally symmetrical grid in three grammars--Palladian,Yingzao Fashi, and Grid--will be used to demonstrate the advantages of the new conventions.