The Product Design Specification (PDS)

The next stage is to transfer all the information so far attained into one of the most important documents, the Product Design Specification. This section and the one that follows outline the tasks involved in creating the PDS to ensure a product designer produces a product design solution that reflects a true understanding of the actual problem and the needs of the user. The PDS is a document listing the design problem in detail; a product designer should constantly refer back to it to ensure his or her design proposals are appropriate.

A PDS splits the problem up into smaller categories to make it easier to consider. The customer or end-user group should be consulted as fully as possible while the PDS is being drawn up as their requirements are of major importance. Any numeric properties in the PDS should be specified as exactly as possible, together with any tolerances allowed on their value.

The PDS is an essential part of all design activity for disciplines such as architecture, product design, and graphic design. In an increasingly competitive global market, product design teams need to produce comprehensive and clear-cut PDSs. It should be noted that the absence of one can cause problems throughout all the subsequent stages of the product development, even up to the final stage, its positioning in the marketplace. Moreover, a poorly constructed PDS will usually lead to a poor design, whereas a good PDS will give the design team a good chance of producing a product that the customer will want to buy and use.

What is a PDS and why write one?

A PDS is a document that sets out exactly what is required of a product, before it is designed. It is essential in the design process; it not only helps the people who design and make the product, but also those who eventually use it. Engineers sometimes overlook the needs and wishes of the customer, but those very people think critically about the products they buy. They may take an interest in design or engineering for its own sake. They certainly will not hesitate to criticize a product if it does not do, efficiently and reliably, what they expect it to. A PDS is therefore also an analysis of what the market will demand of the product.

Things to consider before you start writing a PDS

A PDS specifies a problem, not a solution. A PDS does not preempt the design process by predicting its outcome. Rather, it defines the task by listing all the conditions the product will have to meet. This can involve a good deal of research—into market conditions, competing products, and relevant literature including patents. When you write a PDS, you are defining something that does not yet exist.

Everybody must get involved in the PDS

Once a PDS has been written, it becomes the principal reference for all those working on the design. The PDS must therefore be written in terms that all parties can understand and must be endorsed by all.

A PDS is a dynamic document (subject to change)

A PDS has to be a written document, but it does not need to be engraved in stone. It can be changed. As a rule, the design follows the PDS. But if the emerging design departs from the PDS for some good reason, the PDS can be revised to accommodate the change. The important thing is to keep the PDS and the design in correspondence throughout the design process. In this way, the PDS ends up specifying not just the design, but the product itself.

Elements to cover in a PDS

A comprehensive PDS will comprise anything up to 32 elements (listed in the next section). It is therefore a good idea to write your PDS under these headings, leaving out only those that clearly do not apply. Some of the points overlap, but do not be tempted to skip any of them. Only by checking all of them can you be sure you will not overlook something important. In some projects, however, it may be appropriate to omit a number of elements as they may not be relevant, but if so, this will have been agreed in advance.

Each single PDS element consists of a metric and a value. For example, “average time to clean clothes” is a metric and “in less than five minutes” is the value of this metric. Values should always be labeled with an appropriate unit (e.g. seconds, meters, kilograms). These both form the basis of the PDS.