Friday, 30 November 2012

Whatever Happened to UML?

I first came across UML in the late ‘90s. One of the chaps I was working with downloaded a demo for a tool called Select. We watched as he drew a few boxes and connected them. I can’t remember much more about that particular product but up until that time I had only seen the occasional model in magazines like Dr Dobbs Journal and wondered what it was all about. It inspired me though to pick up a book[1] on the subject (UML Toolkit) and delve into the topic a bit more.

On my next contract I discovered the company had some licenses for Rational Rose ‘98. I initially used it to knock up a few sketches of some stuff I was working on; as much to help me put a legible drawing together as anything else. When we finally started working on a new project I thought I’d try my hand at using some of the other diagrams, to see what else we could get out of it. In particular I was interested in how the Use Case models might play out. I also gave the code generation options a spin to see whether it would be possible to create a skeleton from the model and then keep them in sync.

Of course none of this really panned out. I’m not sure how much was down to the tool and how much was my misunderstanding of what I thought I could achieve, but either way it felt a waste of time. The Use Case modelling was probably more my fault, but it seemed far more work than a set of bullet points and rough notes; I didn’t really see what the model added. The code generation was more likely down to the tool because it just couldn’t represent the relationships in the way I wanted. Useful though the code generation options were for formatting and file structure it just didn’t generate code I liked (for starters it wanted to use pointers everywhere and I wanted references).

But it’s not all bad news. If I look back at my first experiences what really attracted me wasn’t the formal notion of modelling an entire system up front and then pushing a button to generate the code, but the fact that you could knock up a quick diagram that used a representation everyone could understand (eventually)[2]. Seeing the Design Patterns book using UML for its diagrams also seemed to give credence to it’s usefulness. The very idea of Design Patterns seemed to be about taking the “template” and then knocking up a quick sketch where you replaced their class names with the ones from your problem and then standing back to see whether it made sense, or needed further refinement.

I remember having a discussion back then with a colleague about a logging framework we were planning on writing. The Design Patterns book had also taught me to start thinking in interfaces and I was trying to explain how the various parts could fit together and where we could use the Composite and Adaptor patterns to tackle certain problems. My colleague couldn’t immediately see the beauty that this was bringing so I knocked up a UML sketch of the classes and interfaces and gestured about how they would interact. Seeing the light bulb go on as all these concepts fell into place was pretty neat.

Both then and in the intervening years I have found the Class and Deployment Diagrams the most useful. Although I find TDD satisfies for most of my day-to-day work because of the need to refactor and take small steps, when I have a significant new piece to work on I then go back to the sketches and see how it might fit in. I still find that I need to have at least a vague idea of what I’m supposed to be designing before jumping in; it’s more a case of Small Design Up Front than BDUF though.

I’m not suggesting that it’s UML in particular either that I find useful. Really it’s just about drawing pictures to convey an idea. It just happens though that if I’m going to do any diagrams at all then they might as well be done in a tool and format that has some life in it.

That last statement is one that bothers me though. The problem with any tool more niche that something like MS Word is that you wonder if it’ll still be around long enough for you to open the documents again. The kind of diagrams I draw only get an airing every now and then and so you wonder when they will finally pass their best before date. I’ve been using Star UML for the last few years because it’s a native app so it’s very responsive, unlike the Java offerings which lag badly even on modern hardware. Although supposedly Open Source it’s seen little activity since 2005 with just a couple of sideline projects to try and resurrect it in Java.

One of the recent’ish changes to the Doxygen landscape is that you can embed UML diagrams alongside your comments, which can then be consumed with Plant UML. At the recent ACCU Conference one of the last sessions I went to was by Diomidis Spinellis about UML and declarative diagramming tools. The thought of being able to keep the models inside the source code seems to be about the best chance we have of things staying in step. Comments do go stale, but not nearly as easily as a separate document or one outside the source repository.

This also tackles one of the other major problem I’ve had with UML models in the past - merging. Although it’s nice to keep the related diagrams together so that you can browse them, this increases the chances that you’ll have to merge them as they get bigger. The way I saw it you either avoid branching (which is not a bad idea anyway), only update the model on the mainline (likely to forget) or keep the model as a bunch of separate smaller files instead (less navigable). I like to avoid branching anyway and actually I found that keeping the deployment and class models in separate files wasn’t so bad because they are only sketches after all. The prospect of keeping them in the source code just makes the problem pretty much go away. Now the only merge conflicts you have to deal with are the same kind you already deal with anyway.

I am surprised that UML has pretty much disappeared. But then maybe I’m just one of those people who needs pretty pictures to help them visualise a design. Or maybe everyone else just draws on scraps and paper and shoves them in the drawer - I have some of those too. I guess that I fundamentally believe that anything[3] that is of value to me is also probably of value to my teammates and successors, and therefore it’s at least worth a little extra effort to formalise it in some way.


[1] If you’re interested in a book on UML you can’t go far wrong with UML Distilled by Martin Fowler. Here is a link to the book review I did for the ACCU.

[2] The whole “aggregation” thing still confuses me. I’m way too literal and so people who talk about wheels being wholly “owned” by a car just doesn’t make sense to me. What does it then mean when you need to replace a puncture and you get the spare out of the boot and give the broken one to the man at Kwik-Fit to fix?

[3] It used to surprise me when I came across developers that didn’t share their test code and test harnesses (not through any malicious intend I’m sure), especially when you were working on a codebase with no automated tests. Mind you, after after the incident I had on one team perhaps they just learned to keep to themselves.

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