Brought to you today by the letter 'e'.

In my last post, I said you should model verbs, not nouns. I probably exaggerated a bit (I tend to do that) – you shouldn’t completely forget about the nouns. Your verbs wouldn’t have much to do without them. Instead, you should be focused on the verbs and the details of the interactions, not the details of the nouns and adjectives (those will take care of themselves).

Your users want to use your application to get work done. As a I said, gone are the days of simple data entry applications (well, not completely, but certainly anyone building new products isn’t working on solving data entry problems). They want to perform tasks using your application – ordering a book is a task, not a data entry activity. Dispensing a medication, verifying the number of 2x4s in stock, checking a book out of a library – tasks, all.

This is not a new concept. Microsoft published an article about Inductive User Interfaces back in February, 2001 (Inductive was their term for task-based). Tasks have been the focus of various writings about Domain Driven Design, CQRS, and Event Sourcing. Another similar approach is the DCI Architecture, which is a little more formal but also acknowledges the importance of the verbs (or interactions, as they are called).

Which of these approaches, architectures, or techniques you use isn’t overly important. What is important is that you consider the verbs, the events, and the interactions. My last post came from a meeting we had at my company talking about how best to handle data transfer objects. We came to the realization that it was better to have a different DTO for every context, even if they contained the same properties, because as time went on, each of these objects would have their own reasons to change.

This led to trying to determine how best to name these things. How do you differentiate between 6 different OrderDTO classes? The answer is, you don’t – the order isn’t the important part. You focus on what the consumer of the DTO is trying to achieve and use that for the name. This is of course a fairly contrived starting point for a discussion of verbs – I still am starting from nouns (orders are nouns). But it led to further discussion about the way we needed to think about things – in terms of the interactions. If we had started there, we would have had an easier time of things. Fortunately the system under discussion still has a ways to go and we have plenty of time to make use of the lesson.

Special thanks to Matt Otto, who reminded me of DCI Architecture, as well as linked me to this very amusing article that basically makes the same points, although much better.

For most of my career, the “best practice” has been to build applications from the data up. You model the database and then everything will be happy. Its just the way you do it. There is no other way.

So what’s the problem? You end up building applications around what data you need to display and what data you will update. So you show the user all of the data they might need, because you don’t know what they need. You ask for all sorts of data, because you might need it for some scenario. You build screens that they can use to enter any changes that might occur with this data, no matter why those changes are required.

The problem with this approach is there is no “why?”. Why are you showing the user this data? Why are they updating it? What is it that they are really trying to do? You end up with a lot of very obtuse code that is hard to follow, because its only concern is pushing data to the screen from the database, or vice versa. It flows through a lot of logic that you might need in case of various scenarios, but its impossible to know what rules apply to what scenarios, because there is nothing about your code to imply intent.

Back when I started in this field, I was building applications to allow users to put paper forms into databases. There really wasn’t much more logic than that. I was not alone in this – its what most applications did back in the early 90′s. We were trying to build the paperless office, after all.

We can do so much more now. In fact, our users expect it. In order to do so, though, we need to think about the behavior that is expected. What is the user trying to accomplish? Why? What is the intent?

If we examined the behavior, the verbs of the system, instead of just the data (the nouns), we’d have a better understanding of what it was we are trying to build. Our code would be more obvious. The user’s intent would become clear. And then we could build the system the users actually want to use, the one that helps them get their work done in a more efficient fashion. The one that they don’t constantly complain about (OK, that might be a stretch…).

Model behavior by thinking about the verbs. The nouns will follow.