Process.  The collection of business requirements is an art unto itself that requires experienced practitioners and facilitators.  Your business analyst should have a general familiarity with the problem domain, as well as good interpersonal skills.  The analyst should come prepared with a “tool kit” of templates for methodology, process and deliverable work products.  The process of eliciting requirements may take the form of written questionnaires, individual interviews, holistic brainstorming seminars, focused workshops or any and all of these techniques.  Depending on the scope of work, you may have a single analyst or a whole analyst team sited on your premises.  The results of the requirements elicitation process should be documented in work product templates, and classified according to the work methodology.