Software Requirements Models that Work Well Together – Decision Trees and Process Flow Diagrams

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As Requirements Analysts we use Models to paint a picture of the Application we are defining for the developers and eventually to derive the final requirements they will build to. There are many Models that we use to define different aspects of the system – the People who influence the development of the application and eventually use it, the Data that is consumed, transformed and created by the application and the different Hardware and Software Systems that will be used to develop the application.

Some of these Model pairs like Org Chart and Data Flow Diagrams, while useful in their own right are not necessarily complementary. The Org Chart is useful for identifying the Actors and Influencers of the Application. The Data Flow Diagram depicts the flow and transformation of data as it moves from one process to another in the Application. While both these Models are useful and possibly required for your analysis, they are not complimentary. They describe different portions of the Application and using them together does not necessarily enhance your understanding of one or the other.

Other Model pairs work very well together in enhancing one’s understanding of the Application. One Model Pair that I often use together are Process Flows and Decision Trees. Decision Trees work very well in conjunction with Process Flows for the following reasons.

1. They help to simplify Process Flow diagrams by removing complex decision logic from the main flow.

2. Help keep the reader’s focus on the overall flow without getting distracted in the details of one portion of the flow.

3. Make the process flows easier to create and more “legible”. Flows with many decisions and branches are time consuming to create and harder to understand.

A common usage scenario of pairing Decision Trees and Process Flows is when the flows have validation steps. Validation steps are very common is transactional process flows like order creation, quote creation, product configuration and so on. The validation step itself is likely to be complex and will typically require the application to check if all the required data is provided and properly formed. For example, an order entry validation step will check for proper Customer Information, Address, Payment Information and so on. It is certainly not incorrect to put the validation steps into the Process Flow. Doing so can make the flow very busy and messy at this step in the process. I have found that readers do one of two things when confronted with this in a Process Flow and both are bad. They either focus on the “complicated part” and skim through the rest of the flow. Or they do the exact opposite. The net result is that the overall review suffers.

These days, I prefer to keep the branching in my Process Flows to a minimum and use Decision Trees in conjunction with them. As a general rule of thumb, if the Process Flow I am working on is reasonably complex, I try to restrict myself to just one Decision Box in a sequence. In the example above on Order Validation, I would have had just one Decision Box at the validation step titled “Order Valid” and moved forward from there. The different validation steps within the “Order Valid” decision, I would have depicted in a Decision Tree.

The benefits I have found from doing this are as below.

1. The Process Flows are easier to create.

2. The Decision Trees enable me to depict complex logic easily.

3. Splitting out these two aspects enables me to get both right.

4. Lastly, deriving requirements is easier.

Try it and let me know what you think.

 More about decision tress or choosing the right model.

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