Similar to evaluating any project, measuring the success and impact of any data integration project should rely on goals that were defined at the start of the project. In your answer, be sure that you speak about the consideration for the people involved in the project (i.e. customers, sales, IT, engineering) and how success was measured in their eyes. Another great point to touch on in your answer is using the SMART method for setting goals to assure that they are specific, measurable, attainable, relevant and time oriented.
"With any large data integration project that I have managed in the past, success starts with setting realistic yet high standard goals for the project. To do this, I need to make sure that I get input from all key stakeholders in the project. With a recent project, we measure our success in a few different ways. Because of the need set forth by our sales force to be more competitive with our competition in the market, we measured timeliness of the system pre and post integration. Then, to measure the financial impacts of the project, we measured our end of project costs versus what was budgeted. Because our goals were measurable, it was easy to see that the project was a huge success."
"I think that I can best demonstrate this by talking about a recent data integration project we worked on in creating new banking software. At the beginning of the project, we clearly defined the end goals of the project in the data we wanted converted with a set deadline for completion. Our design team added their expectations on their desired workflow following the data conversion. One integration was complete, our goals were easily measured for the project to be considered a success."