Techniques Object-Oriented Design methods D.2.11 Software Architectures Data abstraction General Terms

Object/Relational Mapping (ORM) provides a methodology and mechanism for object-oriented systems to hold their long-term data safely in a database, with transactional control over it, yet have it expressed when needed in program objects. Instead of bundles of special code for this, ORM encourages models and use of constraints for the application, which then runs in a context set up by the ORM. Today’s web applications are particularly well-suited to this approach, as they are necessarily multithreaded and thus are prone to race conditions unless the interaction with the database is very carefully implemented. The ORM approach was first realized in Hibernate, an open source project for Java systems started in 2002, and this year is joined by Microsoft’s Entity Data Model for.NET systems. Both are described here