Such program objects must be storable and transportable for database processing, therefore they usually are named as persistent objects. Another advantage, the object behavior, is related with access to the program objects. That is, a structured type can have subtypes that reuse all of its attributes and contain additional attributes specific to the subtype. Hierarchy within structured complex data offers an additional property, type inheritance. Complex data creation in most SQL ORDBMSs is based on preliminary schema definition via the user-defined type (UDT). The characteristic properties of ORDBMS are 1) complex data, 2) type inheritance, and 3) object behavior. The ORDBMS (like ODBMS or OODBMS) is integrated with an object-oriented programming language. 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. 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 (ORM) software. The basic goal for the object–relational database is to bridge the gap between relational databases and the object-oriented modeling techniques used in programming languages such as Java, C++, Visual Basic. But object databases, unlike relational do not provide any mathematical base for their deep analysis. This brings commonality between the application type systems and database type systems which removes any issue of impedance mismatch. An object oriented database model allows containers like sets and lists, arbitrary user-defined datatypes as well as nested objects. But these types of databases are not optimal for certain kinds of applications. The isomorphism of the relational database system with a mathematical relation allows it to exploit many useful techniques and theorems from set theory. The basic need of object–relational database arises from the fact that both Relational and Object database have their individual advantages and drawbacks.
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