This study focuses on the engineer-to-order (ETO) manufacturing firms that are required to design an entire product to match the requests of their customers. Typical products include machine tools such as machining centers and d rilling machines. Since the customers are not familiar with all product functional specifications, the value of each product functional specification is proposed by the sales staff according to his/her experience. As a result, our target ETO manufacturing firms now face

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... the big problem that the proposed product functional specifications need to be frequently changed not only during the quotation stage, but also after the contract is signed. These changes lead to not only additional costs, but also time loss for design/engineering, production and parts supply departments of the firm. In order to fix the product specifications as soon as possible, in this paper, a product functional structure model is proposed for accurately determining product functional specifications. The model is built by defining customer requirement specifications, product functional specifications, functional structure elements, and evaluating the relationships among the three kinds of specifications. In the first report of this research, drilling machines are taken as an example, and detailed definitions for customer requirement specifications and product functional specifications are determined. Moreover, a constraint detection system is developed to support the sales staff to gather necessary information from the customers and propose accurate product functional specifications to them. By using the product functional structure model, customers' requirements can be defined clearly and impossible specifications of a product can be avoided.