An extension of SQL to support ordered domains in relational databases

The ordered relational model is an extension of the relational model which incorporates partial orderings into data domains. We demonstrate that the ordered relational model is suitable for modelling advanced applications involving tree-structured information, incomplete information and temporal information. We describe OSQL, which is an extension of SQL for the ordered relational model, and show that OSQL combines the capabilities of standard SQL with the power of user-defined semantic orderings. The syntax of OSQL is a minimal extension of SQL and thus it should be easy for current SQL users to adapt to OSQL. Although it is a minimal extension, OSQL allows the users to formulate a wide range of queries, such as fuzzy or temporal, which are either very awkward or impossible to formulate in standard SQL. We also discuss the experimental implementation of OSQL and the further development of the capabilities of OSQL via the notion of an OSQL package in databases, which utilises semantic orderings to define the set of core operations associated with a specific application.