Abstract
The IS-A relationship (the class-subclass relationship) is one of the most fundamental and important properties in an object-oriented (OO) language and OO database management system (OODBMS). Due to the popularity and domination of relational database management systems (RDBMSs) and the fundamental importance of inheritance, supporting IS-A relationships in a RDBMS becomes very desired, and is essential to adapt a RDBMS to more advanced applications. The authors present an extended SQL system called ESQL which facilitates IS-A relation hierarchies in a RDBMS. The proposed ESQL uses constraints to resolve data redundancy and updating abnormality problems that exist in current OO languages such as C++ and Smalltalk, and OODBMS such as GemStone, PostGres, O/sub 2/, Iris, and Orion. Features such as inheritance constraints, subrelation assertions, mappings, and automatic tuple placement into its most specific subrelation are distinct in ESQL. These features are missing in current RDBMSs, OODBMSs and OO languages. >
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