Extension of relational views to derived relations with exceptions

摘要

This paper extends the concept of relational views by allowing exceptions to view definitions via a new construct called derived relations with exceptions (DREs). DREs are a superset of relational views that provides greater capabilities for representing general rules, dealing with exceptional cases and manipulating hypothetical databases. These capabilities are particularly useful in decision support systems, “what-if” situations, in dealing with unexpected data that may violate an integrity constraint and in management of versions. Exceptions are clasified as: internal inclusions, external inclusions and omissions. An extension to the SQL language to support DREs is described as well as its implementation. This extension requires a minimum of changes while providing full functionality.