Web site design and hosting - Persistence layers and alternatives Figure 1.4 A persistence
Persistence layers and alternatives Figure 1.4 A persistence layer is the basis in a layered architecture Presentation layer The user interface logic is topmost. Code responsible for the presentation and control of page and screen navigation is in the presentation layer. Business layer The exact form of the next layer varies widely between applications. It s generally agreed, however, that the business layer is responsible for implementing any business rules or system requirements that would be understood by users as part of the problem domain. This layer usually includes some kind of controlling component code that knows when to invoke which business rule. In some systems, this layer has its own internal representation of the business domain entities, and in others it reuses the model defined by the persistence layer. We revisit this issue in chapter 3. Persistence layer The persistence layer is a group of classes and components responsible for storing data to, and retrieving it from, one or more data stores. This layer necessarily includes a model of the business domain entities (even if it s only a metadata model). Database The database exists outside the Java application itself. It s the actual, persistent representation of the system state. If an SQL database is used, the database includes the relational schema and possibly stored procedures. Helper and utility classes Every application has a set of infrastructural helper or utility classes that are used in every layer of the application (such as Exception classes for error handling). These infrastructural elements don t form a layer, because they don t obey the rules for interlayer dependency in a layered architecture.
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