QueloDB: a Knowledge Based Visual Query System

QueloDB is a prototype tool for querying relational and object-oriented databases. Its most interesting features are based on its capability of reasoning on the semantics of the queries. These features are aimed at improving the interaction between inexpert users and complex databases. The typical user, whom the system is addressed to, is assumed to have no specific experience with data modeling, and no knowledge about the details of database schema. Despite her inexperience, we expect she needs to formulate complex and structured queries. The database is assumed to be ‘complex’, in the sense that it is assumed to materialize a conceptual model with a high number of classes – organized into hierarchies – and relations – with diverse constraints. Thus, it is likely that many query-expressions, even if syntactically correct, are not semantically consistent w.r.t. the given model. Given a formal description of the conceptual model, for example using extended entity-relationship schemata or object-oriented formalisms, QueloDB provides a simple, flexible, and intuitive visual interface that allow the user to: - interactively and iteratively build queries; - interactively explore the semantics of the classes involved; - be introduced gradually only to those part of the schema that can be relevant for her current task of query formulation; - be prevented from making selections that would bring to semantically inconsistent queries; - be provided with simple, but effective, features for query refinement and query generalization