Graphical query formulation for an entity-relationship model

摘要

A query language is defined in which users graphically manipulate entity-relationship (ER) diagrams to formulate queries. The theoretical foundation for the graphical language is algebraic. Each algebraic operator maps an ER diagram to an ER diagram, and every ER diagram represents a possible user query. A set of operators is formally defined and a suggested interactive implementation is given. The set of algebraic operators is both entity-set conservative, which guarantees that a user can interpret any transformed diagram in terms of known entity sets, and relationally complete, which guarantees an acceptable level of retrieval power.