>Let's say you have some software that I want to offer and sell to several clients. Now, the different clients may desire different customizations. At the same time, you would like new versions to benefit all your clients. Or most of them. But if there is too much customization, say, 10 different varieties for 10 different clients, I would have to do any program improvement 10 times, for the 10 different clients.
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>How is this situation handled? Are there any special programming tricks? About the only feasible options I see are
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>1. Abstain from customization; make the program as generic as possible.
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>2. If some clients insist on certain customizations, keep them on older versions. Treat it as a different software (compared to the general, non-customized, version).

We created a "customization" feature in our application that allows us to easily provide customization for any client. Our basic application has "hooks" in numerous places, such as the INIT of all our base classes. These hooks are triggered through a data-driven model that lets us add records to the table to tell it to run certain code from the auxiliary "Custom" app at certain times. The auxiliary custom code can do anything we want such as add or delete fields from a form, manipulate a report, change a SQL Select command, and so on. We also use a class factory to allow us to override any class and run something different for a particular customer. We extended the concept even more by providing a report factory that lets us run a different report for any customer. There's a lot to this customization model and I can't describe it all here, but it's very piossible make your app customizable.