In this paper, we describe our similarity retrieval method for logical schematic diagrams, especially for plants's piping and instrumentation diagrams. In such a diagram, the connection between symbols and lines are essential, and a way to store such data efficiently is presented. And the use of knowledge-base for interpreting diagram structures and retrieving conditions are discussed, to retrieve diagrams suited to a variety of similarity measures. Therefore, we can perform retrieval of diagram data according to its contents, with upgraded man-machine interface functions.
