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.