Summary

The Subscription Management Interface of a SQL-NS application serves as the front end that its users interact with. A well-architectured SMI consists of three distinct layers: a user interface layer that presents visual controls to the user, a logic layer that implements the operations supported by the SMI in accordance with the appropriate business rules and policies, and a data layer in which subscriber and subscription data is persisted.

SQL-NS provides a Subscription Management API that can be used to manipulate subscriber and subscription data in the instance and application database objects. This API consists of a set of classes that represents subscribers, subscriber devices, and subscriptions.

The SMI data layer is created when the ICF and ADF files are compiled to form the instance and application database objects. When building the SMI for an application, you create the logic and user interface layers, as well as any application-specific objects in the data layer required to store subscription information not managed by SQL-NS.

In the logic layer, you implement methods for the operations that the SMI needs to support, as well as helper methods that the user interface layer can use. The implementation of the logic layer uses the classes in the SQL-NS API.

The user interface layer implements the look and feel of the SMI. It provides visual controls that the user can interact with and internally invokes the facilities provided by the logic layer. In some cases, it also invokes the SQL-NS API directly.

In this chapter, we built the logic layer of the SMI for the music store application and looked at a sample user interface implementation. We'll use the SMI built here to enter subscriptions in the music store application as we proceed with its development in the upcoming chapters.