A scoring engine has to actually score something - with your FICO score, it's the risk that you'll default on new credit. Essentially, there are a handful of steps:
- Collect mountains of data
- Decide what you want to know about the data - what do you want to predict?
- Mine the data for a relevant formula that predicts accurately
- Implement the formula in code in a flexible way
Assuming you're asking about step 4, and not about an earlier step in the data mining process, here are some ideas:
- If your formula is simple, you can just code it and allow access to edit the co-efficients (Ax + By + C, as an example, where A, B and C are stored in a database somewhere and are easily updated, and where x and y are some data from your user/customer).
- If you want something highly dynamic, in that you might dramatically change the formula later, a rules engine is one choice, though I'd still lean towards a custom-coded solution that can be easily switched out. Maybe even a DLL with a single function in it that does your calculation, and can be easily replaced if the formula is changed significantly.
If you add some more details, or if you're not quite at step 4 in your mining process, I can suggest some steps for you to take or some reading that might help.