Shape grammars as design tools: an implementation of a multipurpose chair grammar

This paper presents a multipurpose chair grammar and its implementation in the design tool ChairDNA. This tool is oriented for the exploration of design alternatives in the early concept phase of the chair design process. This work addresses two shortcomings within the research area of shape grammars (SGs), namely, the lack of implementation of SGs applied to design domains, and the lack of practical applications in real-life design scenarios. To address these problems, a methodology is proposed for the implementation of a SG (more specifically, a set grammar) into a tool, comprising the translation of the grammar into user-interface elements oriented for design practitioners. By using the proposed tool, the user can add/delete chair components and edit shape parameters, while visualizing the effects on a three-dimensional digital model presented in a variety of CAD applications. Compared with other SG implementations, ChairDNA uses an approach that keeps under control the combinatorial explosion of rule applications, which simplifies the use of the tool by designers that do not have experience in SGs. The generative potential of the tool is demonstrated by generating chairs of different types, and its usability and utility in aiding the designer are evaluated by design students and design practitioners.