Stuart Kent - Software Modeling and Visualization
I just came across this post about XMI from Steven Kelly over at Metacase. In particular, he quotes some figures about usage of the various XMI versions: he's conducted a web search for XMI files out there on the web. The first thing that struck me was how few there are, and secondly how very few there are (34) that use the latest version (2.0) released in 2003.
Steven also makes the observation that XMI is just an XML document containing sufficient information to describe models. Provide your tool stores its models in XML files and/or provides API access to allow you to create models using the API, it's no big deal to write your own importer in code or using XSLT. And if you want to import an XMI file into a domain specific tool, you'd have to do this in any case, because it is very likely your model will be full of stereotypes and tagged values which will need special interpretation that would not be provided by an off-the-shelf importer.
In another post, Steven talks about XMI[DI] which also supports diagram interchange. Another fact: a 20-class diagram takes nearly 400KB. That was a bit of a surprise to me. But it's his observation that "Standards are great, but I think they work best when they arise from best practice based on good theory, not when some committee tries to create something without ever having done it in practice". This strikes a chord with me: it's what I've called premature standardization.
Back in the days when I was an academic and researcher, I used to teach Software Engineering. There are many interpretations of this term, but the focus in my classes was on turning a set of vague requirements into a tangible, detailed spec from which you could reliably cut code. I didn't go much for teaching the text book stuff - waterfall versus iterative and all that - but rather encouraged students to try out techniques for themselves to see what works and doesn't.
Perhaps unsurprisingly given my background, I preached a modelling approach. We'd start out scripting and playing out scenarios (yes, we would actually role play the scenarios in class). I didn't go in for use case diagrams - never really understood, still don't, how a few ellipses, some stick men and arrows helped - but I guess the scenario scripts could be viewed as textual descriptions of uses cases. We'd then turn these scripts into filmstrips. For the uninitiated, these are sequences of object diagrams (snapshots), illustrating how the state of the system being modelled changes as you run through the script. I learnt this technique when teaching Catalysis courses for Desmond D'Souza - indeed, my first assignment was to help Alan Wills, the co-author of the Catalysis book, and now my colleague, teach a week course somewhere in the Midlands. The technique is great, and I still swear by it as the way to start constructing an OO model. From the filmstrips, we'd develop an OO analysis model, essentially an OO model of the business processes. This was class diagrams, plus invariant constraints written in English or more formally, plus lists of actions, plus some pre/post specs of these actions. Then would come the job of turning this model into an OO design model for the (non-distributed, self-contained) program written in Java. And the scripts and accompanying filmstrips could be turned into tests and test data.
Well, that was the theory, anyway. In practice, only a very few students really got it end-to-end, though most picked up enough to still do well in the exam. Reflecting on it now, here are some of my observations:
I now find myself in a role in which most of my time is spent doing what I was trying to teach, though there are a couple of differences:
Here are my observations from the experience so far:
If I was back teaching again, I think I would focus much less on specific notations, and much more on the need to track scenarios through to detailed features, and have coherent specs of the details that communicate the decisions made. I'd also look forward to the prospect of greater automation and use of code generation and software factory techniques. If you've got the right domain specific languages, then models expressed in those languages can replace reams of English spec, and code generators sourced on those models can replace a lot of hand coding. However, they have to be languages matched to the problem, and I suspect that for most systems there's still going to be old fashioned spec work to do.
[edited soon after original post to correct some formatting issues]
I see that the architect of the Guidance Automation Toolkit (GAT), Wojtek Kozaczynski, has started blogging. I worked with Wojtek closely for a couple of months at the inception of GAT (fun it was too), and have been continuing to work with him and his team to merge our text templating technologies - the next version of GAT will contain the new, merged engine, as will the next version of DSL Tools (should be available by the end of the month, and will work with VS2005 Beta2). So soon folks will be able to install both GAT and DSL Tools, and it will be very interesting to see how they get used in combination.
Anyway, his second post is a pocket history of how GAT came to be and makes for an interesting read.
My last post was about this toolkit, pointing at a webcast that gave a demo. But at that point there was no download. Well, now there is. Just visit the GAT workshop site.