This paper presents a comprehensive discussion of the Instance-As-Type (IAT) phenomenon that is observed in the development of complex engineering/product design databases. Basically, IAT reflects a kind of data dependency in databases; in particular it means that a data object appears both in the form of a type and in the form of an instance. As it is well known, uncontrolled data dependencies may lead to information inconsistency and thus severely affect the effectiveness of the product development process. It is therefore very important to develop strategies to cope with IAT in the design of complex engineering databases. The contributions of this paper lie in several aspects. It has provided a more comprehensive description of IAT, including an argument that IAT is in fact not a kind of data redundancy but data dependency. It has also clarified the two and only two feasible strategies for dealing with IAT, i.e., one making IAT absent in a database (strategy 1) and the other preserving IAT by providing a means to control it (strategy 2). The advantages and disadvantages associated with these two strategies have been discussed. Finally, this paper has pointed out that the implementation of strategy 2 can be realized by using general-purpose database management systems (DBMSs) by developing an enhanced program module. A general way to implement this module has also been outlined.

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