PSQL: A query language for probabilistic relational data

Database systems based on the relational model have become very popular for the storage of large volumes of business-related data. Although the relational model provides a great range of advantages over other data models, it was designed to support deterministic data and, consequently, it lacks a comprehensive way for handling uncertain data. However, in all real-world environments, uncertainty in data values is a common occurrence. Therefore, there is a need to extend the relational model so that data uncertainty can be captured explicitly. In an earlier work, we have proposed a probabilistic relational algebra that is a consistent extension of the conventional relational algebra and is reducible to the latter. The contribution of this work is the development of a non-procedural probabilistic query language-structured around the popular SQL-that can be built on top of that algebra. We formalize the extended syntax, provide examples to illustrate the syntax, and examine query formulation from a decision-theoretic perspective (C) 1998 Elsevier Science B.V.