A Critical Path Analysis diagram uses a linear timeline to identify dependent tasks and is particularly used on large, complex projects which may have hundreds of dependent activities. These diagrams highlight dependent tasks that overlap and, therefore, require adjustments to the schedule.
The business requirements document should accurately, and in detail, describe the purpose of the project. It states what is needed to achieve that goal i.e. what is in-scope, what is out-of-scope, any assumptions that have been made, any constraints that have been imposed and expected timescales.