Process Models in Design and Development

Meso-level analytical models

The models described in the previous subsection recommend useful procedures and working steps for design. Although prominent in research and education, they are arguably not specific or detailed enough to guide many real-world situations. For example, in the design of complex products such as aircraft, Step 8 alone from Hubka and Eder’s model (see Fig. 7) typically involves some highly specialised working steps, spans several years, and involves hundreds or thousands of personnel and multiple tiers of suppliers. The meso-level analytical models discussed in this section should be better positioned to provide support in such contexts, because they are concerned with the specific steps that do or should occur within a company and/or design context. They help companies to portray specific DDPs as discrete tasks that interact through well-defined transfers of information to form an end-to-end flow. The premise is that modelling the detail of tasks and their organisation can support design, management, and improvement of meso-level processes.

One factor that delineates families of models within this category is how the relationships between tasks are treated. Our extended review revealed five main subcategories:

1. Task precedence models such as PERT/GERT and the Applied Signposting Model represent interactions between tasks in terms of information flows that define sequences. A relationship between two tasks indicates that the downstream task cannot be attempted until the upstream task has been completed, or progressed by a specified amount.

2. Task dependency models such as the design structure matrix indicate where one task depends on information produced by another. Tasks in design and development often form interdependent clusters, such that there is no obvious sequence to complete them. A dependency model describes such interdependencies but does not indicate how they can be resolved. Possibilities could include making initial estimates for some information and then iterating the tasks until convergence; or undertaking the tasks concurrently with frequent information exchange.

3. Rule-based models such as the adaptive test process represent the DDP as a situated process in which tasks depend on rules concerning their context.

4. Domain-integrating task network models such as the multiple-domain matrix explicitly focus on interactions between a meso-level flow of tasks and other information domains, such as design information.

5. Agent-based task network models such as the virtual design team consider how the meso-level flow of tasks is embodied in interactions between the people who participate in the DDP.

The following subsections discuss these subcategories in turn. For further information on models in this category, the reader is referred to Browning and Ramasesh.