KDE (back when it was still the name of the desktop environment) and our applications historically stood for powerful features and great flexibility and customizeability. This is what our users love about our software, this is why they choose Plasma and KDE software instead of one of the other Free desktop offerings. And it is also something they would fight tooth and nail for if we wanted to take it away (as many a KDE maintainer who dared to remove a feature he thought was unnecessary can tell).

On the other hand, this power and flexibility at times leads to user interfaces that intimidate especially new users if they expose all the features they have to users at once, leading them to avoid our applications altogether. This keeps them from ever experiencing the power which they might enjoy later on, as they use an application for more advanced tasks.

With KDE4 (back then, Plasma as a brand was not born yet), the aim was to keep the power, but do away with the scariness, as the KDE4 Vision states:

“Anything that makes Linux interesting for technical users (shells, compilation, drivers, minute user settings) will be available; not as the default way of doing things, but at the user’s discretion.”

In the design vision and principles section of the KDE HIG, we condensed and evolved this goal into a simple guiding principle:

Simple by default, powerful when needed.

How do we reach that goal?

As the first step, it is necessary to define the target audience and use scenario for an application. Only if we know that, we can define which goals users should be able to reach using the application.

The next step is to define for each goal how likely our target users in the target scenario are to actually have that goal, and how regularly. As an example, when we planned KMail Active (aimed at tablet computers) a year ago, we categorized the tasks we wanted to support in three groups: common, uncommon, and rare.

Only the common actions would be accessible directly in the main user interface. Since the usage scenario we had in mind for KMail Active was “Quickly checking up on new mails on the go or at home on the sofa and occasionally reply”, only those functions relevant to that scenario were planned to be placed in the main UI.

This is how we achieved the “Simple by default goal”:

We optimized KMail Active for users who would rather use KMail Desktop to actually organize their emails by sorting them into folders, or try to retrieve old emails in any folder. However, we recognized that sometimes users may need to retrieve an email from some otherwise rarely used folder or tag or move an email to a certain folder in order to find it more easily later, but don’t have access to a desktop or laptop PC. Therefore a UI to browse through the whole folder hierarchy and the tags (not mocked-up yet) was included in the design, though only visible if users scrolled the view to the left.

The same goes for writing new emails. The default UI for that won’t include things like HTML formatting or adding attachments (since writing longer and more complex emails is not convenient on a device without a keyboard, and users are less likely to have documents they want to send to people on their tablet), but they, too are only presented on demand, not by default. This is the “powerful when needed” part.

This philosophy will guide the designs provided by the VDG, so you will see more examples coming up, soon!

UPDATE: As I’ve seen in some discussions of my post on the Internet (not the comments here) that people apparently thought the screenshot represented the next KMail desktop UI, I’ve updated the screenshot and the caption to make clear what it is.

UPDATE2: Now that this post has become quite popular (2.394 unique visitors so far today!), I felt the need to make clear that – as always with Free Software – all this is a team effort. The original version of the design principles Wiki page was written by Andrew Lake, the user stories for KMail Active were co-written with Heiko Tietze and Michael Bohlender, the design of the mockup was done by Michael Bohlender with my help, and Michael also contributed to the philosophy tagline, by replacing “complex” with “powerful”.