A Comparison of the Hierarchical, Network, and Relational, Database Models
to maintain several “Customers” tables. Data in the network model can be accessed from an entity as opposed to the hierarchical model that requires access from the root entity. The relationships between entities occur through unique set structures. Therefore, although the entities are not duplicated, a unique set structure is required to facilitate each of the one-to-many relationships.
Like the hierarchical model, the network model is also navigational. This poses a big problem in complex designs since the user has to understand the database structure in order to us the database. Furthermore, with a predefined structure like in the hierarchical model, modifying the structure of the database becomes a difficult task. The relational model eliminates many of the problems presented in the network and hierarchical models.
Relational Database Model
The relational model is based on the mathematical set theory. In this model, “data is stored in relations which are perceived by the user as relations” (Hernandez, 1997). Relations are made up of tuples (also referred to as records or rows) and attributes (also known as fields or columns). Each record is identified by a column with a unique value. The order of the rows and columns is of importance. Therefore, the relational model is independent of physical implementation, a quality that makes this model more preferable to the hierarchical and database models. Relationships in this model can be one-to-one, one-to-many, or many-to-many. Regardless of the type of relationship, the model is transparent to the user, that is, the user does not need to understand the physical structure of the database in order to use it.
Relational databases also have their share of problems. The flexibility of the relational model comes with the price of performance speed since the relationships are not predefined like in the case of hierarchical and network databases. Flexibility, also introduces the complexity of enforcing integrity constraints. However, the existence of scientific rules for imposing integrity guarantees that database integrity can be ensured.
Summary
To sum it up, Table 1 below provides a concise analysis of the major differences between the hierarchical, network and relational database models. It is important to note that although the relational model is superior to its predecessors, there are situations that would warrant the use of the older models, especially where the application is simple and not likely to change.
Table 1: Major differences of the hierarchical, network and relational database models
Hierarchical Model Network Model Relational Model
Data access Navigational. Usually accessed from the root. User is required to understand database structure. Navigational. However, data access can start from an entity. User is required to understand database structure. Non-navigational. Database structure is completely transparent to the user.
Performance Faster because structure is predefined. Faster because structure is predefined. Slower because of the flexible arbitrary structure.
DBMS Not compatible with [next page]