Functional specifications documents describe detailed requirements for completing a project (such as creating a web based service or a software or hardware product).
Well-crafted functional specifications follow a process by which the marketing, engineering, design, quality assurance, technical support, documentation, and other relevant departments are all closely involved. The specifications are negotiated, brain stormed, hammered out, and then revised as necessary.
This wide-based involvement is crucial for ensuring that the product is completed on-time, on-budget, and with buy-in from the entire team.
Functional specifications help avoid duplication and inconsistencies, keeping everyone on the same page.
Consequently, they must be updated on a regular basis to keep up with any change in plans. They also provide a means of notifying all members of the team of these changes, and as a reference document for use both before and after the development phase is complete.
Below is a copy of the functional specifications document we created to guide the development of Symantec's Norton DiskLock 4.0, a security application for Macintosh computers.
Click here: techwritinghouse.com/DLfunspec.pdf
Note: This document has been edited to remove confidential information.