EclipseLink/UserGuide/JPA/Introduction/Object-Persistence Impedance Mismatch
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Object-Persistence Impedance Mismatch
Java-to-data source integration is a widely underestimated problem when creating enterprise Java applications. This complex problem involves more than simply reading from and writing to a data source. The data source elements include tables, rows, columns, and primary and foreign keys. The Java and Java EE elements include entity classes, business rules, complex relationships, and inheritance. In a nonrelational data source, you must match your Java entities with EIS records or XML elements and schemas. These differences (as shown in the following figure) are known as the object-persistence impedance mismatch.
Solving Object-Persistence Impedance Mismatch
Successful solution requires bridging these different technologies, and solving the object-persistence impedance mismatch–a challenging and resource-intensive problem. To solve this problem, you must resolve the following issues between Java EE and data source elements:
- Fundamentally different technologies.
- Different skill sets.
- Different staff and ownership for each of the technologies.
- Different modeling and design principles.
As an application developer, you need a product that lets you integrate Java applications with any data source, without compromising ideal application design or data integrity. In addition, as a Java developer, you need the ability to store (that is, persist) and retrieve business domain objects using a relational database or a nonrelational data source as a repository.
EclipseLink addresses the disparity between Java objects and data sources. EclipseLink is a persistence framework that manages relational, object-relational data type, EIS, and XML mappings in a seamless manner. This lets you rapidly build applications that combine the best aspects of object technology and the specific data source. EclipseLink lets you do the following:
- Persist Java objects to virtually any relational database supported by a JDBC-compliant driver.
- Persist Java objects to virtually any nonrelational data source supported by a Java EE Connector architecture (JCA) adapter using indexed, mapped, or XML enterprise information system (EIS) records.
- Perform in-memory conversions between Java objects and XML Schema (XSD) based XML documents using JAXB.
- Map any object model to any relational or nonrelational schema, using EclipseLink and JPA integration with several tools including Eclipse Dali, Oracle JDeveloper, or NetBeans. The Workbench, a graphical mapping tool, is also provided for backward compatibility for projects using the EclipseLink native API.
- Use EclipseLink successfully, even if you are unfamiliar with SQL or JDBC, because EclipseLink offers a clear, object-oriented view of data sources.