The Object Teams Blog

When I write about Object Teams and OT/J I easily get carried away indulging in cool technical details. Recently in the Object Teams forum we were asked about the essence of OT/J which made me realize that I had neglected the high-level picture for a while. Plus: this picture looks a bit different every time I look at it, so here is today’s answer in two steps: short and extended.

Short version:

Extended version:

In software design, e.g., we are used to describing a system from multiple perspectives or views, like: structural vs. behavioral views, architectural vs. implementation views, views focusing on distribution vs. business logic, or just: one perspective per use case.

A collage of UML diagrams

© 2009, Kishorekumar 62, licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.

In regular OO programming this is not well supported, an object is defined by exactly one class and no matter from which perspective you look at it, it always has the exact same properties. The best we can do here is controlling the visibility of methods by means of interfaces.

A person is a person is a person!?

By contrast, in OT/J you start with a set of lean base objects and then you may attach specific roles for each perspective. Different use cases and their scenarios can be implemented by different roles. Visualization in the UI may be implemented by another independent set of roles, etc.

A base seen from multiple perspectives via roles.

Code-level comparison?

I’ve been asked to compare standard OO and OT/J by direct comparison of code examples, but I’m not sure if it is a good idea to do, because OT/J is not intended to just provide a nicer syntax for things you can do in the same way using OO. OT/J - as any serious new programming language should do IMHO - wants you to think differently about your design. For example, we can give an educational implementation of the Observer pattern using OT/J, but once you “think Object Teams” you may not be interested in the Observer pattern any more, because you can achieve basically the same effect using a single callin binding as shown in our Stopwatch example.

So, positively speaking, OT/J wants you to think in terms of perspectives and make the perspectives you would naturally use for describing the system explicit by means of roles.

OTOH, a new language is of course only worth the effort if you have a problem with existing approaches. The problems OT/J addresses are inherently difficult to discuss in small examples, because they are:

1. software complexity, e.g., with standard OO finding a suitable decomposition where different concerns are not badly tangled with each other becomes notoriously difficult.
2. software evolution, e.g., the initial design will be challenged with change requests that no-one can foresee up-front.

(Plus all the other concerns addressed)

Both, theory and experience, tell me that OT/J excels in both fields. If anyone wants to challenge this claim using your own example, please do so and post your findings, or lets discuss possible designs together.

One more essential concept

I should also mention the second essence in OT/J: after slicing elements of your program into roles and base objects we also support to re-group the pieces in a meaningful way: as roles are contained in teams, those teams enable you to raise the level of abstraction such that each user-relevant feature, e.g., can be captured in exactly one team, hiding all the details inside. As a result, for a high-level design view you no longer have to look at diagrams of hundreds of classes but maybe just a few tens of teams.

Hope this helps seeing the big picture. Enough hand-waving for today, back to the code!

Being a part-time release engineer for the Object Teams project I can only agree with every word Kim writes about the job, I wish I could hire her for our project

She writes:

“Nobody in needs to understand how the build works, they just need to push a button. That’s great. Until the day before a release when your build fails with a cryptic message about unresolved dependencies. And you have no idea how to fix it. And neither does anyone else on the team.”

That puts a sad smile on my face and I’d like to add a little quality metric that seems cruel for today’s build systems, but might actually be useful for any software:

One extreme I experienced was in a PDE/Build-ant-build which I had to set to verbose to get any useful answer but then I had to find the relevant error message deeply buried in literally tens of megabytes of log output. Takes ages to browse that log file. Other tools rank towards the other end of the spectrum saying basically “it didn’t work”.

Why is the worst error message relevant? When you hit that worst message it’s close to saying “game over”. Especially when working on a build I’ve come to the point time and again where all my creativity and productivity came to a grinding halt and for days or weeks I simply made zero progress because I had no idea why that system didn’t work and what it expected me to do to fix the thing. Knock-out.

Obviously I hate that state when I make no progress towards my goal. And typically that state is reached by poor communication from some framework back to me.

Real coolness

I know people usually don’t like to work on improving error messages, but please, don’t think good error messages are any bit less cool than running your software on mars. On the one hand we try to build tools that improve developers’ productivity by a few percent and than the tool will give answers that bring that very productivity down to zero. That’s - inconsistent.

I’m tempted to repeat the p2 story here. Many will remember the merciless dump of data from the sat solver that p2 gave in its early days. Some will consider the problem solved by now. Judge for yourself: what’s the worst-case time a regular Eclipse user will need to understand what p2 is telling him/her by one of its error messages.

The intention of this post is not to blame any particular technology. The list would be quite long anyway. It’s about general awareness (big words, sorry ).

Consider the worst case

Again, why worst case? Because the worst case will happen. And it’s enough if it hits you once to easily compensate all the time savings the tool otherwise brought to you.

Communicate!

Framework developers, tool smiths: let your software communicate with the user and let it be especially helpful when the user is in dire need of help.

One small contribution in this field I’d like to share with you: in the OTDT every error/warning raised by the compiler not only tries to precisely describe what’s wrong but it is directly linked to the corresponding paragraph in the language definition that is violated by the current code. At least this should completely explain why the current code is wrong. It’s a small step, but I feel a strong need for linking specific help to every error message.

But first, the software has to anticipate every single error that will occur in order to produce useful messages. That’s the real reason why creating complex software is so challenging. Be it a build system or the “real” software.

Be cool, give superb error messages!