Editor's note: Part 1 of this article was published on 10.19.99.

Did you ever look at one of those huge design documents that barely fit into a four-inch thick, three-ring binder? You assume that by its page count that it must be good. Well, having read some of those design volumes from cover to cover, I can tell you that size does not matter. They are often so full of ambiguous and vague fluff that it was difficult finding the pertinent information. So why does this happen? Because the authors didn’t follow guidelines.

This article is part two of a two part series that provides guidelines that when followed will ensure that your design documents will be pertinent and to the point. Unlike the authors of those prodigious design volumes, I believe in breaking up the design document into the portions appropriate to the various steps in the development process – from concept and proposal to design and implementation. I covered the first two steps in part one of the article, providing guidelines for the game concept and game proposal. This part will provide guidelines for the two heaviest undertakings – the functional specification and technical specification, as well as some guidelines for the paper portion of level design.

Functional vs Technical Specifications

Traditionally in the game industry, there was only one spec. How technical it was depended on who wrote it. Any documentation the programmers wrote afterwards to really plan how they were going to implement it was informal and often remained on white-boards or notepads. Yet in order to ensure the project would proceed without hazard and on time and on budget, the documentation needed to be more technical. Such detailed technical specifications took time – time wasted if the goals and function of the product should change or fail to gain approval.

This problem was tackled as more and more seasoned programmers and managers of business software development moved into games. They brought with them new standards for documentation that helped ensure more accurate plans and less technical problems. They introduced a division in the design document between goals and method and between function and technique. They separated the design document into the functional specification and technical specification. This way, the clients, users or principal designers of the product could review the functional specification and approve the goals and functions of the proposed software – leaving the determination and documentation of the methods and technique up to the technical staff of programmers.

Therefore, the technical staff waited until the functional specification was approved and signed-off before starting on the technical specification. They worked from the functional specification alone, ignoring any design changes that occurred after sign-off unless the spec was updated and a new schedule agreed to. Thus the division saved time for the programmers and gave them more control of the schedule, while still ensuring they had a complete plan for the methods and technique for implementation.

Many companies still refer to the functional specification as the "design document" and yet also produce a technical specification. The term "functional" is a clearer term adapted by businesses and these guidelines to clarify what is expected in the document. Here is a link to a formal definition:

http://webopedia.internet.com/Software/functional_specification.html

In short, what goes into the game and what it does is documented in the functional specification. This is often written from the perspective of the user. How it is implemented and how it performs the function is documented in the technical specification. This is often written from the system perspective. Both form important deliverable milestones in the design stage of the game development process.