c# pdf417 open source Business Logic in the Data Management Tier in Visual C#

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Business Logic in the Data Management Tier
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The classic approach is to put all logic into the database as the single, central repository. The presentation and UI then allow the user to enter absolutely anything (because any validation would be redundant), and the Business Logic layer now resides inside the database. The Data Access layer does nothing but move the data into and out of the database, as shown in Figure 1-10.
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Figure 1-10. Validation and business logic in the Data Management tier
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The advantage of this approach is that the logic is centralized, but the drawbacks are plentiful. For starters, the user experience is totally non-interactive. Users can t get any results, or even confirmation that their data is valid, without round-tripping the data to the database for processing. The database server becomes a performance bottleneck, because it s the only thing doing any actual work. Unfortunately, the hardest physical tier to scale up for more users is the database server, since it is difficult to use load balancing techniques on it. The only real alternative is to buy a bigger and bigger server machine.
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Business Logic in the UI Tier
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Another common approach is to put all of the business logic into the UI. The data is validated and manipulated in the UI, and the Data Storage layer just stores the data. This approach, as shown in Figure 1-11, is very 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 UI
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Unfortunately, in practice, the business logic ends up being scattered throughout the UI and intermixed with the UI code itself, thereby decreasing readability and making maintenance more difficult. Even more importantly, business logic in one form or page isn t reusable when subsequent pages or forms 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 or her data to the web server for any validation or manipulation to take place.
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s Note ASP.NET Web Forms validation controls at least allow for basic data validation in the UI, with that validation automatically extended to the browser by the Web Forms technology itself. Though not a total solution, this is a powerful feature that does help.
Business Logic in the Middle (Business and Data Access) Tier
Still another option is the classic UNIX client-server approach, whereby the Business Logic and Data Access layers are merged, keeping the presentation, UI, and Data Storage tiers as dumb as possible (see Figure 1-12).
Figure 1-12. Business logic deployed on only 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 Logic/Data Access tier for any validation or manipulation. This is especially problematic if the Business Logic/Data Access tier 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.
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 Logic layer that s deployed on the client (or web server), so that it s accessible to the UI layer; and in a Business Logic 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). In the simple cases in which there is no application server, the Business Logic 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 UI 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 UI developer can use to invoke any validation and manipulation logic, and it must also work efficiently with the Data Access tier to get data in and out of storage.
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