When not ranting and raving on this blawg about “great injustices” (LOL) that I perceive are keeping the world from becoming a better place, I design, write, and test real-time radar system software for a living. I use the UML before, during, and after coding to capture, expose, and reason about my software designs. The UML artifacts I concoct serve as a high level coding road map for me; and a communication tool for subject matter experts (in my case, radar system engineers) who don’t know how to (or care to) read C++ code but are keenly interested in how I map their domain-specific requirements/designs into an implementable software design.
I’m not a UML language lawyer and I never intend to be one. Luckily, I’m not forced to use a formal UML-centric tool to generate/evolve my “bent” UML designs (see what I mean by “bent” UML here: Bend It Like Fowler). I simply use MSFT Visio to freely splat symbols and connections on an e-canvas in any way I see fit. Thus, I’m unencumbered by a nanny tool telling me I’m syntactically/semantically “wrong!” and rudely interrupting my thought flow every five minutes.
The 2nd graphic below illustrates an example of one of my typical class diagrams. It models a small, logically cohesive cluster of cooperating classes that represent the “transmit timeline” functionality embedded within a larger “scheduler” component. The scheduler component itself is embedded within yet another, larger scale component composed of a complex amalgam of cooperating hardware and software components; the radar itself.
When fully developed and tested, the radar will be fielded within a hostile environment where it will (hopefully) perform its noble mission of detecting and tracking aircraft in the midst of random noise, unwanted clutter reflections, cleverly uncooperative “enemy” pilots, and atmospheric attenuation/distortion. But I digress, so let me get back to the original intent of this post, which I think has something to do with how and why I use the UML.
The radar transmit timeline is where other necessarily closely coupled scheduler sub-components add/insert commands that tell the radar hardware what to do and when to do it; sometime in the future relative to “now“. As the radar rotates and fires its sophisticated, radio frequency pulse trains out into the ether looking for targets, the scheduler is always “thinking” a few steps ahead of where the antenna beam is currently pointing. The scheduler relentlessly fills the TxTimeline in real time with beam-specific commands. It issues those commands to the hardware early enough for the hardware to be able to queue, setup, and execute the minute transmit details when the antenna arrives at the desired command point. Geeze! I’m digressing yet again off the UML path, so lemme try once more to get back to what I originally wanted to ramble about.
Being an unapologetic UML bender, and not a fan of analysis-paralysis, I never attempt to meticulously show every class attribute, operation, or association on a design diagram. I weave in non-UML symbology as I see fit and I show only those elements I deem important for creating a shared understanding between myself and other interested parties. After all, some low level attributes/operations/classes/associations will “go away” as my learning unfolds and others will “emerge” during coding anyway, so why waste the time?
Notice the “revision number” in the lower right hand corner of the above class diagram. It hints that I continuously keep the diagram in sync with the code as I write it. In fact, I keep the applicable diagram(s) open right next to my code editor as I hack away. As a PAYGO practitioner, I bounce back and forth between code & UML artifacts whenever I want to.
The UML sequence diagram below depicts a visualization of the participatory role of the TxTimeline object in a larger system context comprised of other peer objects within the scheduler. For fear of unethically disclosing intellectual property, I’m not gonna walk through a textual explanation of the operational behavior of the scheduler component as “a whole“. The purpose of presenting the sequence diagram is simply to show you a real case example that “one diagram is not enough” for me to capture the design of any software component containing a substantial amount of “essential complexity“. As a matter of fact, at this current moment in time, I have generated a set of 7+ leveled and balanced class/sequence/activity diagrams to steer my coding effort. I always start coding/testing with class skeletons and I iteratively add muscles/tendons/ligaments/organs to the Frankensteinian beast over time.
In this post, I opened up my trench coat and
showed you my… attempted to share with you an intimate glimpse into the way I personally design & develop software. In my process, the design is not done “all upfront“, but a purely subjective mix of mostly high and low level details is indeed created upfront. I think of it as “Big Design, But Not All Upfront“.
Despite what some code-centric, design-agnostic, software development processes advocate, in my mind, it’s not just about the code. The code is simply the lowest level, most concrete, model of the solution. The practices of design generation/capture and code slinging/testing in my world are intimately and inextricably coupled. I’m not smart enough to go directly to code from a user story, a one-liner work backlog entry, a whiteboard doodle, or a set of casual, undocumented, face-to-face conversations. In my domain, real-time surveillance radar systems, expressing and capturing a fair amount of formal detail is (rightly) required up front. So, screw you to any and all NoUML, no-documentation, jihadists who happen to stumble upon this post. :)
Comprehensiveness is the enemy of comprehensibility – Martin Fowler
Martin’s quote may be the main reason why this preference was written into the Agile Manifesto…
Working software over comprehensive documentation
Obviously, it doesn’t say “Working software and no documentation“. I’d bet my house that Martin and his fellow colleagues who conjured up the manifesto intentionally stuck the word “comprehensive” in there for a reason. And the reason is that “good” documentation reduces costs in both the short and long runs. In addition, check out what the Grade-ster has to say:
The code tells the story, but not the whole story – Grady Booch
Now that the context for this post has been set, I’d like to put in a plug for Simon Brown’s terrific work on the subject of lightweight software architecture documentation. In tribute to Simon, I decided to hoist a few of his slides that resonate with me.
Note that the last graphic is my (and perhaps Simon’s?) way of promoting standardized UML-sketching for recording and communicating software architectures. Of course, if you don’t record and communicate your software architectures, then reading this post was a waste of your time; and I’m sorry for that.
It’s one thing to “bend” the UML to express a design concept that you don’t know how to express with the language, but it’s another thing to “break” it outright. By “break“, I mean drawing old-school, ad-hoc, single-symbol diagrams that all look alike and passing them off as UML class, deployment, activity, etc, diagrams.
By propagating broken UML diagrams out into the world in a sincere, but fruitless, attempt to establish a shared understanding among team members, the exact opposite can occur – mass confusion and an error prone, friction-filled development effort. Even worse, presenting the ad-hoc quagmire to customers and financiers who have a rudimentary education in object orientation and UML can cause them to question the competence of the presenters and the wisdom of their investment choice.
But hey, there’s nothing to worry about. Nobody understands or cares about the UML anyway. Thus, the ambiguity, inconsistency, and conflicts inherent in the design won’t be exposed (or ever traced-back-to) if schedule and cost disaster strikes.
All models are wrong. Some, however, are useful. – George E. Box
In search of economies of scale, centrally planned and controlled economies in nations and corporations tend to create monopolistic providers of goods and services. For example, in corporations, accounting, personnel, and R&D departments are usually deliberately organized as subsidized monopolies. They are subsidized in the sense that the users of their products or services do not pay for them directly; the supplying units are supported financially by funds that are allocated to them from above. The pool from which these funds are drawn is filled by a “tax” allocated from above to the units served. Monopolistic units that are subsidized are generally insensitive and unresponsive to the users of their services, but they are sensitive and responsive to the desires of the higher-level units that subsidize them. These higher level units are even more removed from the units served than the serving units. As a result, they are often unaware of, or unresponsive to, the needs and desires of the internal users of monopolistically provided goods and services. – Russell Ackoff (Ackoff’s Best: His Classic Writings on Management)
OK, time to practice my “bent” UML modeling skills and test your understanding with the class and sequence diagram pair below. The class diagram provides a structural view of a fictional Ackoffian system. The sequence diagram steps through an amalgam of behaviors in a world where monopolies rule. Any questions, comments, critiques, accolades, WTFs?