This project involved the design and implementation of a diagrammer for EXSYS, a recent software product for the design and construction of business systems. EXSYS automates the systems analysis process and, through a series of answers supplied by a user, creates a Data Model of the user’s business environment. The diagrams created using the proposed diagrammer consist of boxes and lines which represent, respectively, the Entities and Relationships which make up an EXSYS Data Model. The reasons why a diagrammer is needed for EXSYS, a description of the environment in which the diagrammer will run, and conventions regarding how diagrams are used to represent Data Model information, are covered in Section 2. A formulation of what such a diagrammer should do is primarily dictated by EXSYS’ users requirements but some more subtle, and difficult to quantify, expectations arise from the fact that diagrams are meant to be read and understood by humans rather than machines. The theoretical considerations involved in designing the diagrammer are discussed in Section 3. A description of the implementation of the diagrammer and some details (such as data structures) of the method of implementation are described in Sections 4. Section 5 discusses the results of the work done on this project and mentions future work needed both to improve on what has been done and to expand the diagrammer to make it a full product. In Section 6, conclusions are drawn as to what has been accomplished in this project, and the usefulness of the project as seen by the wider world (that is, the intended market of EXSYS).