Visual query languages for entity relationship model databases

More and more relational database systems for microcomputers are providing visual interfaces, such as by example (QBE). At the same time, experimental studies are providing more support for the theory that the end users can perform better with the entity relationship (ER) model than with the relational model, for both database design and retrieval tasks. In fact, there are already microcomputer systems for designing the database model based on entities and relationships. The logical development is for future systems to incorporate a visual retrieval module based on the entity relationship model. To provide guidelines for the design of these new interfaces, many proposed visual query languages (VQLs) are analysed and compared from the user's viewpoint. The analysed features include ER concepts, interaction modes, model diagram transformations, condition specification, aggregate functions, and output organisation. Different competing approaches adopted by the VQLs are also examined. The survey results enable designers of future VQLs to build on existing techniques. It also identifies major approaches for human-factor researchers to empirically determine the best for users.