Human interface guidelines (HIG) are software development documents that offer application developers a set of recommendations. Their aim is to improve the experience for users by making application interfaces more consistent and hence more intuitive and learnable.
The quality and acceptance of a guideline depends to a large extent on its set-up. A good structure guarantees quick access to the information the reader looks for. Additional, links to the rationales behind the guideline as well as alternative solutions are helpful. A HIG should not only include widgets and their appearance but also core usability goals, generic design specifications, and user demands. To manage all these aspects we have chosen to adopt the "Universal Model of a User Interface" by Bob Baxley (2003) as basis for the new KDE HIG. This model has been slightly adjusted to account for more recent approaches to visual design guidelines.
The central aim of KDE HIG is to create a consistent experience across the software compilation. This means to apply the same visual design and user experience as well as consistent access and predictable behavior of common elements in the interface -- from simple ones such as buttons and icons up to more complex constructions, such as dialog boxes.
The model consists of three tiers, each of which is made up of three layers:
Structure contains concept, design vision and principles, task flow and organization. It should answer question like: What constitutes KDE software?, Who is the user of KDE software?, and Where do we want to go in future?
Design Vision and Principles
There are almost always multiple solutions to any given user interface problem. Consistency in the choice of solutions and, ultimately, the experience of the user, is guided by a Design Vision. As such, the design vision is aspirational by definition; it is a high level description of the desired user experience in not just one application, but across multiple KDE applications and the KDE workspace. A set of Design Principles are derived from the design vision as a means to provide more specific guidance on how to achieve that desired user experience.
The conceptual model is the most fundamental aspect of the interface, describing the relationship between the interface and the outside world. The purpose of the conceptual model is to draw on the user's past experiences so they can readily understand basic operations and accurately predict functionality.
The organizational model describes how the system's content and functionality are ordered and categorized. Also known as the information architecture, the organizational model encompasses both the classification scheme as well as the model of association, hierarchy versus index for example.
Behaviour includes viewing and navigation, editing and manipulation and user assistance. All elements of the Behaviour layer must satisfy the Design Principles. This layer is more like 'traditional' guidelines, addressing questions like: How should a button behave in case of...?, or What widget do I have to use for a selection of one out of a few items? All HIGs assume that the controls referenced in the following "Implementation" sections are used. Therefore they only contain guidelines for aspects which can be changed by the developer, to keep them as concise as possible. If you feel your application needs something which the referenced standard KDE or Qt widget does not provide, don't create your own custom replacement, because it might violate the best practices which are implemented in the standard widget. Instead, ask the KDE HIG team for advice on how to solve your specific problem.
Viewing and Navigation
The Viewing and Navigation layer encompasses the wide variety of behaviors and operations that allow users to navigate the interface and affect its presentation.
Editing and Manipulation
The Editing and Manipulation layer contains the behaviors that result in permanent changes to user's stored information. ... Behaviors in this layer can often be recognized by the following traits: they result in permanent, stored changes; they require an implicit or explicit save operation; and they typically require validation of the input data.
Interface elements that inform users of the application's activity and status, as well as elements dedicated to user education, are all contained in the User Assistance layer. This includes online help, error alerts, and status alerts.
Presentation deals with visual design of the user interface -layout, style and text. It's all about the appearance of the application including the platform style's margins and spacing, Colors, fonts, icon designs, etc. These questions primarily concern designers, developers, translators and the promotion team.
The various design decisions governing the placement , ordering ans spacing of onscreen elements are expressed in the Layout layer. In addition to providing an ordered visual flow, the Layout layer also supports the Behavior tier by arranging elements in a manner that helps communicate behavior, importance, and usage.
The Style layer is concerned with emotion, tone, and visual vocabulary. Because it is the most visible and concrete aspect of an interface, it typically accounts for people's first impression of a product. Style is influenced by the use of color, the design of icons throughout the interface and the use of typography. All elements of the Style layer must satisfy the Design Principles. This allows the style to change as necessary while still preserving the user experience secured by the Design Principles.
Contained within the Text layer are all the written, language-based elements of the interface. This includes the labels used to represent the organizational model, the names of the input and navigational controls contained in the Viewing and Navigation layer, and the alert messages and help text used by the User Assistance layer.