Some Issues of Using Higher Degree Relationships Between Entities in Relational Databases

Abstract

The creation of a database model begins with the construction of a conceptual model, which is a high-level abstract
model of data. Conceptual model usually described as Entity-Relationship Model, which represents some subject area data using
entities and relationships between them. In the logical data model, the essence of the conceptual model is specified, if necessary,
new entities and relationships are added, key attributes are defined. The process of normalization the logical model reduces data
redundancy and ensures data integrity. In the physical model, the logical model is transformed for a specific database system,
where data storage mechanisms are considered. The degree of a relationship indicates the number of entities that are associated
with that relationship. Depending on how many entities are participated in their association, there are considered: unary, binary,
ternary and higher-degree relationships. Ternary relationships add complexity to the database schema, can lead to redundant
data and may result in more complex queries. There are: 1:1, 1:N, N:M relationships between instances of the entities. In the
relational database model 1:1 and/or 1:N binary relationship are allowed, therefore, higher-degree relationships should be de
composed to binary relationships to prevent data loss and/or the creation of non-existent records. Ternary and higher-degree
relationships are rare, but their consideration helps us to build a complete database model. A database specialist intuitively
constructs already normalized binary relationships. The article discusses an example of a ternary relationship and the process of
its transformation into a set of binary relationships.