Object-relational Mapping, including: Java Data Objects, Hibernate (java), Object-relational Impedance Mismatch, Toplink, Ibatis, List Of ... Apache Openjpa, Apache Cayenne, Propel (php)

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More info: Object-relational mapping (ORM, O/RM, and O/R mapping) in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language. There are both free and commercial packages available that perform object-relational mapping, although some programmers opt to create their own ORM tools.