Vision

Software projects don't get started out of the blue. Someone has been pondering ideas for a new product for a while or convinced himself that a given problem needs a real solution by enhancing an existing software or developing a new one. This person, it may be a group as well, is the visionary. She knows best how the solution should look like, what the criteria for success is and when it doesn't make sense to pursue the project any further.

Well run projects have as well a project sponsor somewhere in the organization. That's a person backing up the visionary so that she can run the project and makes sure the project does not get cut off when unforeseen problems arise.

What a good vision document should contain

The vision document should explain why the project is being done, what the project is about and when the project will be a success. Success should be seen as organizational success not technical success.

Should it be long?

It should be as long as it needs to be but don't write a novel. It will be displayed on the dashboard and the purpose is that everybody can glance at it to be remembered of the goals for the project.

Is it static or a living document?

If ever possible it should be a living document and be updated once new information becomes available. Be careful about drifting into a completely new project while the current one is not yet done though.

What should I do, if large parts of the original vision don't apply anymore?

Changing your charted course slightly in order to incorporate things you learned is ok - steep turns or going into the opposite direction is not. If you see that the current vision document state something that doesn't apply anymore and you would have to drastically change everything, then you may want to consider to halt the project and start a new one. Stopping and starting again creates a clear sign for everybody. You may want to hold a meeting with all team members (stakeholders, product owner, programmers, testers) so that everybody has a chance to fully understand why the vision changed so drastically and what the new one is going to be.

Beware of multiple visions Sometimes a vision is very broad or simply imprecise. Be careful of such visions. They will get your project into trouble later on. Better try to reduce it to a single vision or realize that you are in fact dealing with multiple projects. In that case someone needs to decide which one to conduct first.