Tomcat web server - CHAPTER 1 Understanding object/relational persistence relational databases, where
CHAPTER 1 Understanding object/relational persistence relational databases, where interaction with the database occurs via an intermediate language (SQL) and data independence from a particular application is the major concern. For background information on object-oriented databases, we recommend the respective chapter in An Introduction to Database Systems (Date, 2003). We won t bother looking too closely into why object-oriented database technology hasn t been more popular; we ll observe that object databases haven t been widely adopted and that it doesn t appear likely that they will be in the near future. We re confident that the overwhelming majority of developers will have far more opportunity to work with relational technology, given the current political realities (predefined deployment environments) and the common requirement for data independence. 1.3.5 Other options Of course, there are other kinds of persistence layers. XML persistence is a variation on the serialization theme; this approach addresses some of the limitations of byte-stream serialization by allowing easy access to the data through a standardized tool interface. However, managing data in XML would expose you to an object/hierarchical mismatch. Furthermore, there is no additional benefit from the XML itself, because it s just another text file format and has no inherent capabilities for data management. You can use stored procedures (even writing them in Java, sometimes) and move the problem into the database tier. So-called object-relational databases have been marketed as a solution, but they offer only a more sophisticated datatype system providing only half the solution to our problems (and further muddling terminology). We re sure there are plenty of other examples, but none of them are likely to become popular in the immediate future. Political and economic constraints (long-term investments in SQL databases), data independence, and the requirement for access to valuable legacy data call for a different approach. ORM may be the most practical solution to our problems. 1.4 Object/relational mapping Now that we ve looked at the alternative techniques for object persistence, it s time to introduce the solution we feel is the best, and the one we use with Hibernate: ORM. Despite its long history (the first research papers were published in the late 1980s), the terms for ORM used by developers vary. Some call it object relational mapping, others prefer the simple object mapping; we exclusively use
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