RML™ Requirements Model 5 - The Data Flow Diagram (DFD)

The Data Flow Diagram (DFD) is a very useful part of the Requirements Modeling Language (RML™). The Structured Analysis Wiki contains a great explanation of how to create a DFD, so I’m not going to cover that information here. Instead, I’m going to provide one answer to the question “How do I know when to use a DFD?” This answer comes from my own (unique) view of the world, so some of you probably won’t relate to it, but others will--I’m sure there is at least one more out there…

Sometimes I have what I think of as an "equation" in my head. In vague terms, I may be thinking “Customer Data + Product Data + Input from Sales Rep + Taxes = Order”. But that's not really right, nor is the equation a good representation of the information.

And, the “equation” also misses a few other particulars about creating an order that I’d like to convey: Sales Reps update customer data, the Finance staff maintains the rules for the tax calculations, and orders flow to the Order Fulfillment system after creation.

The data flow diagram is great for representing all of this. Here’s my “equation,” expressed as a data flow diagram:

I have found that business users, as well as developers, react well to this model—it provides a “big picture” with which to begin a conversation about creating an order. It paints exactly the picture I want to convey and validate when I’m thinking “Customer Data + Product Data + Input from Sales Rep + Taxes = Order”.

Display this picture, and you’ll get some interesting questions and comments:

• How is customer data populated initially?


• Does the order fulfillment system update the order store with information about the fulfillment of the orders?


• Where does the product data come from?


• Are all of the tax rules manually entered, or is there also an electronic source for them?


• And, maybe, “No, that’s wrong, updating customer data isn’t a separate process. Customer updates need to automatically flow out of changes made when creating the order.”
  

One note: it doesn’t have to be technically perfect to be useful. I often provide “conceptual” DFDs, in that I intentionally provide conceptual, but not technical information. For example, conceptually, there is a “products” data store. Technically, there may be multiple stores: product list, product descriptions, etc. The important thing is that they work together to provide product data. Developers and architects are very receptive to this; they understand I’m illustrating the behaviors of the system without defining the implementation (which, after all, is their job). Oh, and how does the audience know it is conceptual? I put the word “conceptual” in the title!

You may notice I didn’t number my processes. That’s because I rarely decompose them and many people tend to take the numbering as ordering. So, for my usage, numbering adds confusion rather than clarity.

Happy diagramming!

Related Articles:

How To Choose A Software Requirements Model

Six Requirements Models For Agile Projects

Live from RESFQ: The Requirements Object Model (ROM), part 3

Today we have an example to illustrate what I’ve said in the past two posts from Tuesday's setup for the ROM and Wednesday's definition of the ROM.

Let’s say in this scenario we have an online gaming company that historically has only built complex role-playing games. Now let’s say the head of product management wants to build a Yahtzee game. Here’s the process to go back and figure out what the problem is that someone thinks Yahtzee will solve, working our way to the top until we get to a Business Objective.

Note the problem at the top of this diagram finally becomes one that relates to money: The competition is still growing and we aren’t. And the business Objective can now be written to quantify the desire: 25% growth in markets other than 15-30 year olds.

Now that we have a business objective, we can define strategies. There may be 5 or even 100 business strategies and someone must select the ones to be implemented. In this case, 2 possible strategies include building a game for 7-13 year olds and advertising to the retirement community. Out of that, we can believe that Yahtzee is a valid product concept, as long as they develop it to target that 7-13 year old user group.

Finally, we can complete the rest of the ROM by crisply defining our product concept (Online Yahtzee), success metrics (7-13 year olds rate the game fun), and guiding principle (create a social environment). Then we can take on the fun task of defining features that fit within this definition.

If you follow this approach, you will have a constant guide in your Business Objectives to ensure that you are creating features that you need, but only features that you need, to achieve the business value of the project.

Live from REFSQ’09: The ROM, Experiences with a Requirements Object Model

What follows is a summary of the paper I wrote with James Hulgan (also from Seilevel) and presented at REFSQ’09 last week. The paper is titled “Experiences with a Requirements Object Model”. You can get the actual paper here.


Most software projects we’ve seen develop features that don’t add value or they don’t build what they actually do need in order to achieve the intended business value. This leads to project that are over budget, late, and often canceled because they don’t really satisfy the needs. Fundamental to this, most project teams don’t know the Business Objectives that tell them why they are doing the project in the first place, so it’s not surprising they have a hard time picking the right features to develop.


Business Objectives are hard to elicit. When teams get an answer like “increase profitability” they are complacent to stop there because they don’t want to or know how to push people to give the hard answers.


Our paper discussed the basic terminology as described by many industry experts to describe this “thing”. They use business objectives, goals, needs, business requirements, user requirements, etc. And there are subtle differences behind each of these from person-to-person. But for our work, we are using “Business Objective” to mean: the desired metrics the business seeks to meet in order to solve the business problems.


Terminology is just a small part of the problem, but the bigger issue is this: If you ask a project team why they are doing this project, they often have no concrete idea. They may have a vague phrase associated with it such as “We are reducing operating costs”. Sometimes we hear them say that they are sure the executives know because there was a business case developed – but the project team has not seen it. It’s as if you can develop the business case, start the project, and never need to look at it again. And this is where the problem lies. The Business Objectives, probably in that very business case, should be driving the feature set developed.


We were looking for a model to use to identify and represent these, as well as to train our people on to elicit them. Out of that came the ROM – Requirements Object Model.


Tune in tomorrow for a description of the ROM!

How To Choose A Software Requirements Model

Do you find that you're always trying to use process flows on your projects, but they just don't seem to fit your needs?

Do you need to start modeling requirements, but can't quite decide what models to use?

There are quite a few requirements models out there to choose from, ranging from the mundane (process flow), to the amorphous (use case) to the exotic (fishbone diagram). Knowing which models may be most helpful to you can be a bit tricky, but the following tips can help!

Choosing the Right Software Requirements Model

If your application has:

• Lots of User Interaction - useful models can be Org Charts, Use Cases, System Context Diagrams
• A Complex UI - useful models can be Org Charts, Use Cases, Wireframes
• Lots of Involvement with Different Systems - useful models can be System Context Diagrams, Data Flow Diagrams
• Data Processing - useful models can be Entity Relationship Diagrams, Data Flow Diagrams, System Context Diagrams

And don't stop with these - there are many other models to explore! Take the plunge, and break away from process flows today!

Check out these detailed explanations.

• State Tables
• Decision Trees
• Click Action Response Tables
• Data Dictionaries