Overview:
This artifact contains the definition of the stakeholders' view of the product to be developed, specified in terms of the stakeholders' key needs and features. It contains an outline of the envisioned core requirements for the system.

Purpose:

This artifact provides a high-level, sometimes contractual, basis for the more detailed technical requirements that are visible to the Stakeholders. It captures the essence of the system by describing high-level requirements and design constraints that give the reader an overview of the system from a behavioral requirements perspective. It serves as input for the project-approval process, communicates the fundamental "what and why" for the project, and provides a plan against which all future decisions should be validated.

Main Description:
This artifact provides a complete vision for the software system under development and supports the contract between the customer and the development organization. Every project needs a source for capturing all Stakeholders' expectations.

This artifact is written from the customers' perspective, focusing on the essential features of the system and acceptable levels of quality. The artifact should include a description of what features will be included, as well as those considered but not included.