Willingness to share incomplete information has long been identified as a necessity for concurrency in design. This can perhaps be best understood in terms of the lean production practice of reducing batch sizes, which belongs with DSM as a technique for restructuring the design process. Sequential processing results in part from the implicit rule that only completed design work is advanced to others. In terms of the beam penetration case, suppose the design team members agreed up front on work sequence, which would start by Team Member A providing just that information needed for Team Member B to calculate what he needs. B would in turn release that information to C, allowing C to do work, etc.
The Lean Construction Institute recommends producing such a work sequence by having the team responsible for the work being planned to work backwards from a desired goal; i.e., by creating a ‹ pull schedule ›. Doing so avoids incorporation of customary but unnecessary work, and yields tasks defined in terms of what releases work and thus contributes to project completion. So doing reduces the waste of overproduction, one of the seven types of waste identified by Taiichi Ohno.
The Lean Design Group case described below (Set Based Design) is an excellent example of the benefits of implementing this strategy. Deferred commitment is a strategy for avoiding premature decisions and for generating greater value in design. It can reduce negative iteration by simply not initiating the iterative loop. A related but more extreme strategy is that of least commitment; i.e., to systematically defer decisions until the last responsible moment10; i.e., until the point at which failing to make the decision eliminates an alternative. Knowledge of the lead times required for realizing design alternatives is necessary in order to determine last responsible moments. Such knowledge now tends to be partial or lacking.
POSITIVE VS NEGATIVE ITERATION IN DESIGN
Glenn Ballard