Retrieving information from data flow diagrams

For reverse engineering, we need tools that can extract information from documents written before routine digital storage was feasible. Documents contain both text and diagrams; data flow diagrams play a prominent role in software documents. Using current techniques, it is possible to recover the information in a data flow diagram by scanning the printed document and processing the data obtained. Feature extraction and syntax analysis enable the construction of a validated, formalized model of the data flow diagram. Understanding, however, requires a semantic interpretation. We describe a semantic model for data flow diagrams using general techniques that can be applied to other kinds of diagram. We argue that a semantic model is an essential component of a document understanding system; without a semantic model, it is difficult or impossible to extract useful information from a document.