Several criteria are normally used to classify DBMSs. The first is the data model on which the DBMS is based.
The main data model used in many current commercial DBMSs is the relational data model.
The object data model was implemented in some commercial systems but has not had widespread use. Many legacy (older) applications still run on database systems based on the hierarchical and network data models.
The relational DBMSs are evolving continuously, and, in particular, have been incorporating many of the concepts that were developed in object databases.
This has led to a new class of DBMSs called object-relational DBMSs
We can hence categorize DBMSs based on the data model: relational, object, object-relational, hierarchical, network, and other.
There are several types of database management systems. Here is a list of seven common database management systems: