Extending the View Updatability of Relational Databases from Set Semantics to Bag Semantics and Its Implementation on PostgreSQL

View support is one of the most attractive features of relational databases from both theoretical and practical points of view. However, as views are not base relations stored in a database but merely definitions of queries issued to a database, the updatability of views poses a difficult dilemma known as the view update problem. To resolve the problem, many theoretical investigations, namely, the syntactic, semantic, interactive, and intention-based approaches were conducted, with the intention-based approach being the most promising. In practice, SQL-92 standardized a necessary and sufficient condition for updatable views, but its updatability is limited. Although new criteria for updatable views were standardized in SQL:1999, its implementation seemed to be hard. To benefit relational database users, we aimed to implement the intention-based approach for a relational database management system. However, we faced two issues in doing so. Therefore, in this study, we present the positive solutions to these problems. First, as theoretical works are based on set semantics and SQL standards on bag semantics, whether the intention-based approach can be extended to bag semantics or not should be investigated. Second, the approach should be implemented on PostgreSQL, which is the prevalent open source relational database management system in the world.