Yesterday, I started to grasp more comprehensively the relationship between personas, use cases and scenarios.

While trying to piece this together, I drew what used to be a simple diagram. But then it got a bit out of hand:

The reality and the dynamics a UI designer observes and manipulates

Download diagram: PDF, Openoffice ODG

First off, there’s reality. That is to say, this is not scientific research. In a small scale guerilla usability project, we do not pretend it is, much. Still, we observe reality and gather knowledge about the users. Iteration in testing and also in interviews must serve as our backup against which we check that our conclusions are hitting their target: we take the knowledge we find to the user interface and to our generalized conclusions, and then verify with our users.

Use cases

In a sense, modeling use cases equals doing actual UI design: the main difference is in the abstraction level. Use cases will be the actual hard ground when drawing prototypes, representing the idea or ideal about what the UI should be like. That is, what should be possible to accomplish with it, and how.

When designing the actual user interface, the designer takes all the use cases (=the goals), and merges them using his/her creativity and experience. As the use cases may conflict, the resulting user interface is usually some sort of a compromise between the different use cases. Also platform restrictions pose threats to the ideals: technology requirements (no dependency on Javascript in this case) and needing to conform to existing UI conventions would be examples of this.

In the case of this project, I have so far been thinking about the word “use cases” mainly from the point of view of the old user interface – I have understood it roughly as the functionality of the UI, which is to be transferred to the new UI, just better enabling the users’ scenarios (better enabling users to do their tasks). However, this is actually an overly computer-centric approach to use cases, and basically incorrect. More importantly, as is obvious in terms of the definition, use cases take the functionality of the program and model the user in interaction with that functionality.

There are several ways to see use cases. First, when we look at the current UI, you can see three different sets of use cases, from ideals to reality:

  • ideal use cases: how the software developers think the software should be interacted with
  • observed use cases: gathered by seeing real users (UI testing or otherwise) use the current UI. This is a subset of the next one:
  • the real-world use cases of the interaction that is taking place with real users and the current UI


When we just have the use cases of existing software, we do not get very far. At best, with testing, we see the problems users are having with the current software. What we do not see, is whether or not we are even trying to solve the right problems.

Enter scenarios. That is: independent of the application and its UI, what is it that the user aims to achieve, and what is the way s/he does it best?

How do we find out? Talk to the users. It may be scary at first. They are people, after all! But go ahead and try – turns out that people are actually glad if someone wants to learn about what they need to make their lives easier.

Whenever you talk with actual users about their actual tasks and goals, you are in the sphere of scenarios. But the hard part is taking the scenarios and making them somehow digestible pieces. That is: you look at what the users tell you, and tear it in pieces until they are atomary, that is, single actions (you might want to observe this in terms of GTD’s Next Actions: visible, physical actions). It is not just the tasks you need to find out about, but what affects accomplishing those tasks: patterns, goals, skills, attitudes, and environment (as stated in Cooper’s article about personas, link below).

Getting somewhere

So now we have a set of use cases from the old software. Then we have a set of scenarios describing the actual environment, tasks and goals of the user. Now, we try to match them: scenario 1a fits with use case 1c, and actually, also with use case 1d (that is, the user can do the same thing in more than one way in the application). But then with scenario 1b, the user has to do a task in an unnatural order of subtasks or can’t do it at all because it is too hard for him/her or because it cannot be done at all.

And once we get that far, we can take those differences, and start writing new use cases. That is, designing the interaction that the application should facilitate. Once sufficient iteration has been achieved or the deadlines are too close, we can state: We know – well enough – the interaction and whatever affects what that interaction should be like – now let’s get to business, the actual UI.

Oh yeah, almost forgot – something brilliant: Perfecting Your Personas