Sequence of Requirements Analysis Tasks

The sequence in which the tasks associated with Requirements Analysis are performed is not etched in stone. Nor are the tasks themselves necessarily performed in isolation from one another. For example, tasks are documented while they are being performed; a data flow diagram is often created while conducting interviews; user views are frequently sketched while examining the existing database(s), and so forth.
Requirements analysis in systems engineering and software engineering, encompasses those tasks that go into determining the needs or conditions for a new or altered product and taking account of the possibly conflicting requirements of the various stakeholders.
Requirements analysis is critical to the success of a development project. For this reasons requirements must be documented, actionable, measurable, testable, and related to identified business needs or opportunities.
Requirements can be architectural, structural, behavioral, functional, and non-functional.

This bold admonition may seems like a quote from a project manager who holds extreme views on work ethic, but in fact, sometimes your life does depend on how you collect your data. Time series data provides many such serious examples. But let us begin with something less life threatening, such as: where would you like to spend your vacation?
Suppose you have been living in Seattle, Washington for two years. You have enjoyed a lovely summer, but as the season moves into October, you are not looking forward to what you expect will once again be a gray, chilly, and wet winter. As a break, you decide to treat yourself to a short holiday in December to go someplace warm and sunny. Now begins the search for a good destination. You want sunshine on your holiday, so you start by seeking out reports for rainfall in potential vacation places. Reasoning that an average of many measurements will provide a more accurate report than just checking what is happening at the moment, you compare the yearly rainfall average for the Caribbean country of Costa Rica (about 196 cm) with that of the South American coastal city of Rio de Janeiro, Brazil (117cm). Seeing that Costa Rica gets almost twice as much rain per year on average than Rio de Janeiro, you choose the Brazilian city for your December trip and end up slightly disappointed when it rains all four days of your holiday.