With most Java applications, developers have to deal with issues related to data persistence, mainly because of interfacing with a relational database. But as the application is based on an Object model and the database on a Relational model, an Object-Relational Impedance mismatch arises, with both systems taking a different view of how entities interact with each other. Objects have an implicit sense of identity denoted by references to memory location, while Relations have an explicit sense of identity denoted by the primary key of the table relationship attribute. This creates a gap between the operation of Objects and Relations. And it's for developers to bridge this gap.
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