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 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 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.