| Summary: | The retrieval methods use the explicit elements and associations which appear in a structured design representation, without requiring an understanding of the designs or their application domains. They depend instead on simple similarity measures concerning the basic representation elements, and integrate this basic evidence within the structured representations. Structure is handled dynamically, so that fragments are defined by the best-matching level for each query. The propagation of evidence through the structure of fragments allows different types and levels of representation to be related. These principles are developed are evaluated within an IR framework consisting of textual information, not least since text can and does express design information, especially concerning experience and the design process. Moreover, IR provides standard test collections to quantify retrieval performance. Although usually based on fairly long passages of unstructured text, such a collection can be used to evaluate the suggested approach to retrieving structured mechanical design fragments, which is difficult to assess directly. Rather than transferring the structured representation to flat text, which would lose information, a structure is imposed on a textual test collection and an analogy drawn between structured design representations and structured text. The results show that formalised knowledge structures such as classifications are not necessary for retrieving design information. Instead, informal knowledge and 'obvious' connections between representation elements can lead to improved retrieval performance, according to the standard IR measures of precision and recall. However, connections are not always applicable in every context, and retrieval performance suffers if any ambiguity in the representation elements or their similarity measures is not resolved before making connections. The representation structure forms a convenient context for this process of resolving ambiguity. There are several applications of this work. One is in Design Reuse, initially via a retrieval system which suggests standard components to replace specially-designed parts. Allowing for imprecision means that it can be used relatively early in the design process.
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