The Concept of Databases

Hierarchical database structure

This is a tree-like structure for presenting information. Its peculiarity is that each node at a lower level has a connection to only one node at a higher level. Let’s look, for example, at a fragment of the hierarchical structure of the database “Institute”:

It is clear from the structure that one department can have several faculty members. This relationship is called “one to many” (one department – many teachers). But if we try to add student groups to this structure, we need a “many to many” relationship;

(one faculty member can work with many groups, and one group can learn from many faculty members), and there cannot be such a link in a hierarchical structure (because the link can only be with one node at a higher level). This is the main disadvantage of such a database structure.

The network structure of the database

This is essentially an extension of the hierarchical structure. Everything is the same, but there is a “many to many” relationship. The network database structure allows us to add groups to our example. The disadvantage of the network model is the difficulty of developing serious applications.

Relational Database Structure

All data are represented as simple tables, divided into rows and columns, at the intersection of which the data are located. We will talk about this in detail in the next articles, here we want to note that this structure was a real breakthrough in the development of databases.

Object-oriented and hybrid databases

In object-oriented databases the data is stored in objects, which is very convenient. But today such databases are still very common, because they are inferior to the relational ones in performance.

Hybrid databases combine the capabilities of relational and object-oriented databases, so they are often called object-relational. An example of such DBMS is Oracle, starting from version 8.

Undoubtedly, such databases will be developed in the future, but for now the priority is given to relational structures. This is why we will study them in the next lessons.