About the Frameworks Series
Besides the Java language, a world of Java frameworks exists. These frameworks can afford substantial improvements in programmer productivity and enhance the quality, performance, reliability, and interoperability of different Java applications. Fortunately, many of these popular and widely used frameworks are open source projects, so anyone can benefit from them if he can invest some time learning when and how to use such frameworks. This article is the second installment in the frameworks series and aims to introduce persistence frameworks in general and the open source Java persistence framework, Castor JDO, in particular.To read previously published article in this series, follow this link: Frameworks.
Most enterprise applications need access to a relational database. The Java standard for accessing relational databases is the JDBC APIs that utilize SQL as a data manipulation language. This approach of directly accessing a relational database from an object-oriented Java application was shown to be inefficient and introduces a problem called "object-relational impedance mismatch," or simply "impedance mismatch" for short.
The article continues at http://www.developer.com/db/article.php/3355151