This is a question I see asked a number of times in various forums. It is one of those “It Depends” sort of topics, but is one that I think is worth discussing here. In this post, I’ll give you my perspective on how I’ve used it in my projects.
Probably the most important thing you have to understand is, “Why are you using UML at all?” – assuming you are in the first place, or are considering using it in the near term. As the old saying goes, a picture is worth a thousand words. A UML diagram is simply a picture of part of a (potentially) complex system. And sometimes the best way to break down the complexity is through pictures.UML diagrams convey structure or behavior through pictures of classes and their interactions. It supports numerous diagram types to break down the system into various views, which can be combined in order to represent the system from different angles in order to help bring perspective and clarity.
Organized in a logical way, the UML diagrams you create help to tell the story of the system you are developing. The $64,000 question is, “Who is the story’s primary audience?”. Generally, the answer to that is the development team that is building the application. However, with the success of Agile, many teams feel that UML is unnecessary, or at best, it’s used in ad hoc ways with very lightweight and high level diagrams – maybe even temporarily on whiteboards during meetings. It’s simply viewed as a means to convey a concept or outline. I certainly agree with the spirit of that. UML can help to speed up the team because it helps to bring understanding and consensus through a shared view of what they’re building. How lightweight or detailed your diagrams are, or even if they are persisted, should be a decision you make based on the team’s appetite and ultimately the overall value add to the team and project. Flexibility is the key.
And no matter what the long term goals are, the short term benefit of an increase in velocity is probably the most valuable takeaway you will realize by using UML.
In order to gauge the right amount of diagraming to provide to the team, I have used the sprint retrospectives to reflect on this with the team and arrive at the right answer. The teams that I’ve worked on have all been comprised of a mixture of experience levels. Typically, the less experienced team members or newer team members gain the most benefit from the diagrams. The more experienced team members still benefit from them, though, as they almost always help to disambiguate the design details. The net effect is that it helps to level the playing field across the team and improves communication and ultimately productivity. I have almost always chosen to persist the diagrams in a modeling tool – even if for no one else but myself for future reference.
In a highly Agile team where practices like TDD are used, the use of UML may likely be perceived as an impediment. You can make a pretty well supported argument that this viewpoint is right. The design should emerge from the creation and iterative refactoring of code and unit tests to flesh out the details. Up front design using UML is the opposite of that approach. Unless you consider it from the perspective of general high-level architectural point of view that is. The UML diagrams you use can describe many higher level aspects of the system like: patterns; guidelines on organizing system components; describing the layers of abstraction; deployment details; or other high-level details. Let TDD do what it’s best at – creating flexible and resilient designs at a low level of detail.
Most development teams have a certain amount of turnover throughout their lifetime. The reasons for this are myriad, but the bottom line is that you will need to bring new team members up to speed at various points in time throughout the life of your project. If the system that they are working on is reasonably complex, the UML diagrams that you created to convey your design concepts to the original team members can be an excellent way to help the new team members understand what they are working on. I am a firm believer that every team member should get the big picture. They shouldn’t be relegated to some dark corner of the application with little or no visibility into how it all fits together. Use of tools like UML helps to bring everyone up to speed, which is a good thing.
A common argument that I have heard against using UML is that like most documentation it will always be stale when compared to the code. I would say that this is generally true. There are many ways to deal with this, but probably the best way is to just accept that fact and understand that the main use of the tool is to help people understand the system. If the diagrams are too far out of alignment with reality, update them. Most tools support reverse engineering. Use it to refresh the details and update the diagrams. Your future team members will thank you. Just don’t get bogged down in the minutia of sync’ing code with models all the time. That’s one of the quickest killers of usefulness.
In the end, I will also yield with an “It Depends” answer for the original question. Since no two teams and no two projects are exactly alike, I’d say you will have to gauge the right answer based on your current circumstances. For me, I’ve always relied on UML as a means to reducing complexity and organize thought around the structure and design of complex systems. Let your team help you to decide the right answer.
Happy Modeling
