There is mainly 2 database   ORDBMS and OODBMS


An Object-Relational Database (ORD) or Object-Relational Database Management System (ORDBMS) is a database management system similar to a relational database, but with an object-oriented database model: objects, classes and inheritance are directly supported in database schemas and in the query language. In addition, it supports extension of the data model with custom data-types and methods.
One aim for this type of system is to bridge the gap between conceptual datamodeling techniques such as ERD and ORM, which often use classes and inheritance, and relational databases, which do not directly support them.



Another, related, aim is to bridge the gap between relational databases and the object-oriented modeling techniques used in programming languages such as Java, C++ or C#. However, a more popular alternative for achieving such a bridge is to use a standard relational database systems with some form of object-relational mapping software.

Whereas traditional RDBMS or SQL-DBMS products focused on the efficient management of data drawn from a limited set of data-types (defined by the relevant language standards), an object-relational DBMS allows software-developers to integrate their own types and the methods that apply to them into the DBMS. ORDBMS technology aims to allow developers to raise the level of abstraction at which they view the problem domain. This goal is not universally shared; proponents of relational databases often argue that object-oriented specification lowers the abstraction level.


An object-relational database can be said to provide a middle ground between relational databases and object-oriented databases (OODBMS). In object-relational databases, the approach is essentially that of relational databases: the data resides in the database and is manipulated collectively with queries in a query language; at the other extreme are OODBMSes in which the database is essentially a persistent object store for software written in an object-oriented programming language, with a programming API for storing and retrieving objects, and little or no specific support for querying.

Many SQL ORDBMS's on the market today are extensible with user-defined types (UDT) and custom-written functions (e.g. stored procedures. Some (e.g. SQL Server) allow such functions to be written in object-oriented programming languages, but this by itself doesn't make them object-oriented databases; in an object-oriented database, object orientation is a feature of the data model.

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