Hello Kelly,
I think that who is responsible for this function is the Product Manager. Like MOF docs talks:
"The primary team role type driving envisioning is Product Management, whose main goal is to ensure that the customer’s identified business needs are addressed."
"Product Manager acts as the customer advocate, helps drive shared project vision, manages customer expectations, sets overall goals, identifies customer needs, determines project requirements, and produces the vision/scope document."
Hope that helps
Regards,
Cleber Marques
MOF Brazil Project: Simplifying IT Service Management
www.mof.com.br | www.clebermarques.com | www.clebermarques.com.br