Object-Relational Mapping (ORM)

Object-relational mapping (ORM) is a programming technique in which a metadata descriptor is used to connect object code to a relational database. Object code is written in object-oriented programming (OOP) languages such as Java or C#. ORM converts data between type systems that are unable to coexist within relational databases and OOP languages.

ORM resolves the object code and relational database mismatch with three approaches: bottom up, top-down and meet in the middle. Each approach has its share of benefits and drawbacks. When selecting the best software solution, developers must fully understand the environment and design requirements.

In addition to the data access technique, ORM's benefits also include:

• Simplified development because it automates object-to-table and table-to-object conversion, resulting in lower development and maintenance costs
• Less code compared to embedded SQL and handwritten stored procedures
• Transparent object caching in the application tier, improving system performance
• An optimized solution making an application faster and easier to maintain

ORM’s emergence in multiple application development has created disagreement among experts. Key concerns are that ORM does not perform well and that stored procedures might be a better solution. In addition, ORM dependence may result in poorly-designed databases in certain circumstances.