Reasoning Methods for Designing and Surveying Relationships Described by Sets of Functional Constraints

Abstract

Current methods of database schema design are usually based on modeling the real world as entity (or object) classes with relationships among them. Properties of relationships can be described by semantical database constraints. One of them is functional dependency, which has a key role in traditional database design. The three basic types of binary relationships that can be described by functional dependencies are one-to-one, one-to-many and many-to-many. They can also be expressed by common graphical languages like the Entity-Relationship (ER) graph. However, relationships defined among more than two entity classes (ternary, quaternary, etc.) are usually not investigated and the common graphical tools lack expressive power regarding them. We show that the variety of relationship types is rich for higher arities and propose a simplified formalism for functional constraints as well as graphical and spreadsheet reasoning methods for handling sets of functional constraints that also help by relationship design.