Business Logic in the Interface Control Layer in Visual C#

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Business Logic in the Interface Control Layer
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Another common approach is to put all of the business logic into the interface control code. The data is validated and manipulated by the interface control code, and the Data Storage and Management layer just stores the data. This approach, as shown in Figure 1-11, is common in both Windows and web environments, and has the advantage that the business logic is centralized into a single tier (and of course, one can write the business logic in a language such as C# or VB .NET).
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Figure 1-11. Business logic deployed with only the Interface Control layer
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CHAPTER 1 DIS TRIBUTED ARC HITE CTURE
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Unfortunately, in practice, the business logic ends up being scattered throughout the application, thereby decreasing readability and making maintenance more difficult. Even more importantly, business logic in one form or page isn t reusable when subsequent forms or pages are created that use the same data. Furthermore, in a web environment, this architecture also leads to a totally non-interactive user experience, because no validation can occur in the browser. The user must transmit his data to the web server for any validation or manipulation to take place.
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Note
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ASP.NET validation controls at least allow for basic data validation in the interface, with that validation automatically extended to the browser by the ASP.NET technology itself. Though not a total solution, this is a powerful feature that does help.
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Business Logic in the Middle (Merged Business and Data Access Layers)
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Still another option is the classic UNIX client/server approach, whereby the Business and Data Access layers are merged, keeping the Interface, Interface Control, and Data Storage and Management layers as dumb as possible (see Figure 1-12).
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Figure 1-12. Business logic deployed only on the application server Unfortunately, once again, this approach falls afoul of the non-interactive user experience problem: the data must round-trip to the Business/Data Access layer for any validation or manipulation. This is especially problematic if the Business/Data Access layer is running on a separate application server, because then you re faced with network latency and contention issues, too. Also, the central application server can become a performance bottleneck, because it s the only machine doing any work for all the users of the application.
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Sharing Business Logic Across Tiers
I wish this book included the secret that allows you to write all your logic in one central location, thereby avoiding all of these awkward issues. Unfortunately, that s not possible with today s technology: putting the business logic only on the client, application server, or database server is problematic, for all the reasons given earlier. But something needs to be done about it, so what s left What s left is the possibility of centralizing the business logic in a Business layer that s deployed on the client (or web server), so that it s accessible to the Interface Control layer, and in a Business layer that s deployed on the application server, so that it s able to interact efficiently with the Data Access layer. The end result is the best of both worlds: a rich and interactive user experience and efficient high-performance back-end processing when interacting with the database (or other data source).
C HAPTE R 1 DISTRIBUTED A RCHITEC TURE
In the simple cases in which there is no application server, the Business layer is deployed only once: on the client workstation or web server, as shown in Figure 1-13. Ideally, this business logic will run on the same machine as the interface control code when interacting with the user, but on the same machine as the data access code when interacting with the database. (As discussed earlier, all of this could be on one machine or a number of different machines, depending on your physical architecture.) It must provide a friendly interface that the interface developer can use to invoke any validation and manipulation logic, and it must also work efficiently with the Data Access layer to get data in and out of storage.
Figure 1-13. Business logic centralized in the Business layer The tools for addressing this seemingly intractable set of requirements are mobile business objects that encapsulate the application s data along with its related business logic. It turns out that a properly constructed business object can move around the network from machine to machine with almost no effort on your part. The .NET Framework itself handles the details, and you can focus on the business logic and data. By properly designing and implementing mobile business objects, you allow the .NET Framework to pass your objects across the network by value, thereby copying them automatically from one machine to another. This means that with little extra code, you can have your business logic and business data move to the machine where the Interface Control layer is running, and then shift to the machine where the Data Access layer is running when data access is required. At the same time, if you re running the Interface Control and Data Access layers on the same machine, then the .NET Framework won t move or copy your business objects. They re used directly by both tiers with no performance cost or extra overhead. You don t have to do anything to make this happen, either .NET automatically detects that the object doesn t need to be copied or moved, and thus takes no extra action. The Business layer becomes portable, flexible, and mobile, and adapts to the physical environment in which you deploy the application. Due to this, you re able to support a variety of physical n-tier architectures with one code base, whereby your business objects contain no extra code to support the various possible deployment scenarios. What little code you need to implement to support the movement of your objects from machine to machine will be encapsulated in a framework, leaving the business developer to focus purely on the development of business logic.
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