When considering a product, it is important first to consider the overall architecture of the product to end up with a coherent design. Product architecture defines the said product in the context of aligning physical requirements to functional requirements. This is similar to other design methodologies, such as axiomatic design, and is wholly compatible with many of those systems.
Karl Ulrich, in the early 1990s, attempted to qualify product architecture in his paper on the role of product architectures in manufacturing. Ulrich discussed overall product architecture, the taxonomy behind these product architectures, and various attributes of these architectures. Ulrich completes his writings with a summation of research opportunities in the 1990s .
Product architecture, as defined by Ulrich, is the arrangement of functional elements as they are mapped to physical components. Ulrich also discusses the interfaces between physical components as aspects of the product architecture . Ulrich suggests using standardized function description language along the same lines as Stone et al. . This would allow for greater reproducibility among designs within the same product architecture. Standardized nomenclature also reduces errors from having to learn a new product architecture framework that may have eccentricities that are unknown to the new designer.
The functional structure can be defined at multiple levels of abstraction. It may be more useful in early product development to start defining functional structure in the most generic terms possible to eliminate the risk of inadvertently removing design options before beginning the design process.
As the design process progresses, the functional structure will become more clearly defined. Ulrich recommends the classical approach to functional element modeling. This approach utilizes signals, materials, forces, and energy interactions using the verb-noun relationship common in other design methodologies .
Ulrich distinguishes modular architecture and integral architecture. This relates to the coupling between physical components regarding change management and design modification. Ulrich recognized that decoupled interfaces result in a product architecture that is more resilient to change . Dependencies found in integral architecture systems may result in a small change having large ripples throughout the product. This is a non-ideal situation in most designs.
Modular architectures may be further subdivided into four primary styles. Slot architecture utilizes interchangeable parts that are decoupled yet still required to achieve the relevant functional requirement. Bus architecture allows for greater modularity in that parts are interchangeable and expandable rather than required. Sectional architecture uses a single interface style in a ring configuration . These product modular architecture styles may be a framework in the early concept design stages.
Ulrich considers the impact of change within the framework of product architecture. Products may be upgraded, added to, adapted, worn, consumed, or reconfigured. This requires a modular architecture style to maintain the product in a usable configuration . Products may change the existing product generation or subsequent generations. Each subsequent generation should be evaluated for the reincorporation of standard features and parts when possible to reduce retooling costs.
Product variety may be managed through product architecture. As variety drives consumer excitement, it is critical to ensure that adequate variety exists within the consumer space to drive product sales. As variety drives cost increases, the product architecture must account for maintaining maximum variety at minimum cost.
Similar to the reuse of preceding generation product parts, standardization of product components helps to drive lower costs in the manufacturing process. Maintaining adequate product architecture documentation allows for improved identification of opportunities for incorporating standardized parts. Products using a modular product architecture are more likely to benefit from standardized part incorporation.
Others would later use Ulrich's work as a framework for several design methodologies and systems. The careful application of Ulrich's techniques would drive future design method improvements for years. By understanding the historical context of modern design methodologies, design engineers can better place modern research in context to the developments found in the past.
 Ulrich, Karl. "The role of product architecture in the manufacturing firm."Research policyÂ 24.3 (1995): 419-440.Â
 Stone, R. B. and Wood, K. L., 2000, "Development of a functional basis for design," Journal of Mechanical Design, Vol. 122, p. 359. - 370