From the client's perspective, the survey is represented as Questions and Routing XML. The Question XML can easily generate the question representation and display the questions to users. It is a bit more difficult to use the Routing XML's routing items to determine the survey flow order.

The JavaScript sourced Expression Evaluator provides methods for processing the If routing item expressions, that change the interview flow. The Expression Evaluator provides a library that is accessible to third party applications. Because IBM MobileFirst Platform Studio uses JavaScript for application logic, it can be used in the creation of applications that target both Android and iOS. JavaScript also provides options for creating Web interviews that can locally run survey routings, which minimizes round-trips to the server.

The Expression Evaluator defines Categorical, InterviewValue,FunctionLibrary, and Expression JavaScript classes.