Performance

Especially for Web-based applications, performance requirements generally revolve around having acceptable response time. Response time is the amount of time a user waits after requesting an action before seeing a result. All users, including you and me, would like to see instantaneous response times from Web sites, but with current technology, this expectation is not realistic. Within the .NET Framework, particularly with ASP.NET, many performance enhancements have been added for additional benefits in this area, but in reality, the following major factors affect response time:

• Limited bandwidth

• Server or network capacity

• Server traffic

• Application-processing constraints

In the Web environment, many of these factors are outside the scope of your application, so performance will always be an issue. It would be unrealistic for users with 28K modems to expect immediate responses from a site handling their requests. Beginning in the requirements phase and continuing all the way through implementation, you must concentrate on the areas within your control. The key factor is to avoid unnecessary complexity or overhead that further degrades performance. For example, you might have a requirement to minimize the time needed to process an online order so that customers don't abandon orders because they take too long to complete. Another requirement could be for the application to launch and close quickly. To satisfy these requirements, you might have to include in your design the constraint that you will be able to transfer only small amounts of data from the server. By recognizing requirements and constraints early in the process and taking advantage of the tools at your disposal, you have a much better chance of maximizing your users' satisfaction.

Other areas could be considered performance-related requirements; for example, you might want to gauge performance by how often the system is up and running. For the purpose of this discussion, however, these areas are actually related to other operational requirements. As you'll see in the next section, gauging how often the system is up and running is actually an availability requirement. Other scalability and accessibility issues might also seem performance-related but are actually factors in those operational areas.