How to draw a good diagram of a business workflow? What software?

Question

I want to create an illustration for a product purchase wizard, and I want to illustrate the way user interacts with the wizard. It's basically a simple flowchart or a simple workflow:

1. User starts the wizard
2. User selects product
3. User should check the availability of that product (manually)
4. If the product is available, then the next button is enabled, else it's disabled
5. If user change the product type, then the next button should be disabled
6. User goes to the next step
7. Based on the product type, a different UI is shown to him in the next step
8. He should adjust some other settings, ...

I started creating a sequence diagram, but soon it proved not to be a good fit. Then I changed to activity diagram, again no success.

What type of diagram should I choose to illustrate this flowchart (which is full of conditions, branching, state management, user interaction and more)? Do we have such a general diagram at all? What software should I use?

Update: To clarify further, I'd like to draw a diagram of a scenario rather than a workflow.

Answer 1

Rather than trying to find a general diagram and only producing one diagram, consider using multiple diagrams and types of diagrams to capture specific information.

I would consider using an activity diagram for modeling the high level flow control of the application and the business processes that happen. For particular (the most important) use cases, consider using a sequence diagram and/or communication diagram to drill down a little deeper and show interactions between objects. A state diagram can also be used to show valid state transitions throughout the operation of the application.

The idea is that you don't want to show everything on a single diagram. For example, you don't want to get into particular method calls on an activity diagram and you don't want to show multiple use cases on a sequence diagram. If you did, it would be too difficult to read, and the documentation wouldn't add any value.

Answer 2

In addition to UML Activity Diagrams, there is Business Process Modeling (BPMN 2.0) - This is an accepted method/standard of showing business process flow.

The notation is simple to grasp and there free tools. The interesting this is that some tools allow you to measure the performance by running simulation of the process and some tools generate ready to run applications from the diagrams without writing code.

Also BPM uses swim lanes and actors much like UML Activity Diagram but they are not the same.

One of the good tools is Bizagi at : Bizgi BPM

If you want to see a tutorial, see: [Resources1]2

The net is full of other resources ofcourse.