Decomposition of Database Classes under Path Functional Dependencies and Onto Constraints

Abstract

Based on F-logic, we specify an advanced data model with object-oriented and logic-oriented features that substantially extend the relational approach. For this model we exhibit and study the counterpart to the well-known decomposition of a relation scheme according to a nontrivial nonkey functional dependency. For decomposing a class of a database schema the transformation pivoting is used. Pivoting separates apart some attributes of the class into a newly generated class. This new class is declared to be a subclass of the result class of the so-called pivot attribute. Moreover the pivot attribute provides the link between the original class and the new subclass. We identify the conditions for the result of pivoting being equivalent with its input: the expressive power of path functional dependencies, the validity of the path functional dependency between the pivot attribute and the transplanted attributes, and the validity of the onto-constraint guaranteeing that values for the transplanted attributes can be referenced from the remaining part of the original class.