Applications Are More Than Code

This article is the second in my series around migrating an application or what is sometimes referred to as a Lift and Land.  

Applications are the final product after numerous iterations of business, marketing, financial, and resource decisions. Those decisions impact how large your lift is going to be and understanding those decisions is just as crucial as rewriting the code base. If the previous budget was cut short and only half the features exist, it's important to discuss that before starting on the project. If the previous developer loved Ruby and the one before had only PHP experience, you will most certainly end up decrypting the same logic in two code bases to ensure they contain the same business logic. Assigning a Business Analyst allows you to have one lead who understands the application thoroughly and is the primary project business expert.  

Whom have you used to make sure your application doesn't lose it's current business features when rewriting it?