You are designing an n-tier solution that includes a Windows Presentation Foundation (WPF) client application. The WPF application connects to a middle-tier server that runs the data access layer. The data access layer connects to a Microsoft SQL Server 2008 database and to a mainframe-based database.
The mainframe-based database will be replaced in one year. You have the following requirements:
Centrally manage all database connections.
Minimize changes to the code base when the database is replaced.
Ensure that the WPF application will not need to be redeployed when the database is replaced.
You need to recommend an approach for designing the data access layer.
What should you recommend?
A. Create a data access layer class that uses a database factory class to access all databases. Add the connection string information for the databases to the configuration file for the WPF application
B. Add the connection string information for the databases to the configuration file for the WPF application. Implement one class in the WPF application for each data source.
C. Create a data access layer class that uses a database factory class to access all databases. Add the connection string information for the databases to the configuration file for the data access layer class.
D. Add the connection string information for the databases to the configuration file for the WPF application. Implement a database factory class from within the WPF application.
