We make use of a refined E-R model to represent the contents of pictures. We propose remedies to handle mismatches which may arise due to differences in perception of picture contents. An iconic user interface for visual query construction is presented. A naive user can specify his/her intention without learning a query language. A function which computes the similarity between a picture and a user's description is provided. Pictures which are sufficiently close to the user description, as measured by the similarity function, are retrieved. We present the results of a user-friendliness experiment to evaluate the user interface as well as retrieval effectiveness. Encouraging retrieval results and valuable lessons are obtained.>

Safety-critical systems are not only difficult to build, but also difficult to debug because they often have strict timing constraints and non-deterministic behavior. A correct and precise specification reduces the effort spent in testing and debugging the implemented system. This paper presents techniques of specification debugging and issues related to it. We introduce an approach to the debugging of a specification in FRORL (Frame and Rule Oriented Requirements Language), which supports non-determinism and non-monotonicity in a system. The approach aids the user in detecting and correcting the possible faults which can arise not only when writing the specification, but also after the verification of the specification.