Case-Based Reasoning and Case-Based Design have been proposed to utilize knowledge of previous design solutions to understand or solve current design problems. Case retrieval is often performed on the basis of verbal indexing systems, whereas in design the use of graphic representations is predominant. Case retrieval therefore, requires verbalization from the designer, which can interrupt the flow of thought during design. This paper aims to demonstrate how the theoretical work on generic representations in architectural design can form a graphic indexing scheme for cases that are graphic representations. The paper outlines three techniques: a decision-tree for graphic unit recognition, a query composition algorithm, and a look-up table for case retrieval. These three techniques are worked out in the context of a Case-Based Design Aid System.