The data layer can be broken into three sublayers in most applications. They are the data storage layer, the data access layer, and the service agent, as shown in Figure 1-1. The data storage layer provides the mechanism for storing and managing your application data, and the data access layer provides the logic needed to retrieve and manipulate data. | CHAPTER 1 ENTERPRISE APPLICATIONS 7 thinking of the logical separation of components and tiers when referring to the physical separation of components. The typical high-level layers of an application are the presentation layer the business logic layer and the data layer. However the needs of an application do not stop with these components of an application. As previously mentioned an application may also need components to handle security application configuration exception handling logging application deployment and so forth. The specific application components will be determined based on the functional and technical requirements of the application. However as an enterprise grows and applications are developed it will soon become apparent that all these applications share common functionality between them. This common functionality is the perfect candidate for common enterprise framework components. Figure 1-1 shows the different components that are typically used in an application. In the following sections I ll introduce several of the most common components. Components of an Application Data Layer Supporting Data Storage Layer Components Data Access Layer Service Agent Application Configuration g Domain Logic Layer Securttlf o Q. E Exception fg Domain Workflow Layer Service Layer Management g Logging Instrumentation Presentation Layer n . Caching User Process Layer User Interface layer Cryptography Figure 1-1. Components of an application Data Layer The data layer can be broken into three sublayers in most applications. They are the data storage layer the data access layer and the service agent as shown in Figure 1-1. The data storage layer provides the mechanism for storing and managing your application data and the data access layer provides the logic needed to retrieve and manipulate data. The service agent is like the data access layer but instead of accessing a data storage layer the service will access another domain process such as a web service or COM
