An essential part of designing user interfaces consists of communicating about system behavior and functionality that has ultimately to be provided in the user interface in a user-friendly manner.

To transfer knowledge regarding system behavior / system functionality, a variety of methods can be used. Often, use case descriptions and screen scribbles are employed to provide the required information. When a user interface designer has a kickoff meeting for a project, for example, a stakeholder can scribble a screen that would provide essential system functionality so that the user interface designer gets a quick impression of certain system aspects. During requirements engineering, use case descriptions might have been created that are handed to the user interface designer to get a feeling for workflows that are carried out and the desired user-system interaction.

Both ways of documentation have their advantages and drawbacks.

Use Case Descriptions

Use cases are helpful for organizing information in a structured manner and for giving an impression of the user-system interaction. They can describe interactions, constraints, alternatives and the dynamics of user-system interaction in a formalized manner and are relatively easy to understand since they are written in (semi-)prose.

On the downside, good use cases need some time (and experience) to write so that, for example, during a meeting, no one “quickly writes a use case” to make clear certain aspects of system functionality. In addition, it takes time to read and understand use cases, so their “accessibility” is not immediate.

Screen Scribbles

Screen scribbles, on the other hand, are very easy to access since they are graphical in nature and do not require the recipient to read lots of text. In addition, they can also be created very quickly in an “on-demand” like fashion to illustrate what a system is supposed to do, for example which options the system provides for the user and which objects are affected by choosing a particular option.

The drawback to scribbles is that they can severely limit the creativity of the user interface designer. The limitations can be twofold:

• Concretely visualizing interface elements in an early stage may put the user interface designer on a certain “track” that is hard to get off again. Even though he may be aware that this danger exists, it make take some time for him to be able to make a “fresh start” with new ideas for the user interface and to “forget” about the early scribbles.
• The limitation of the user interface designer’s creativity may also result from other stakeholders that are involved in the design process. This can occur when people are fixated on scribbles that have been created early on and therefore oppose against “changing” the interface later because they would see that as a step backwards. This may especially happen in projects with tight schedules during which a strictly incremental approach is taken so that user interface design in later stages must build on artifacts that have been created earlier in the process while “discarding” interface designs is not allowed. (“We already have an interface to start with, so let’s build upon that.”) In this case, the main goal of the scribble in the early project stage – namely to communicate certain requirements and functions, but not to be regarded as a design solution – is simply ignored.

Practical Approach

In practice, a combination of the two methods can be fruitful, especially when all persons involved are informed about the strengths and weaknesses of each method.

To quickly generate and discuss ideas (for example during meetings or in presentations), scribbles can be helpful. When using them, it should be made clear that they simply serve as basis for discussion and that they may be used as a basis for detailed design, but that this does not necessarily have to be the case. Their primary use is as a communication tool and as such they may not determine the later design of the user interface more than a textual use case description does.

Use cases can be helpful when describing the dynamics of user-system interaction (for which, otherwise, a series of scribbles might be necessary). They can also go into more depth than scribbles by describing, for example, conditions and alternative paths that can hardly be captured in scribbles.
So, for the user interface designer or usability engineer, an important task is to choose the appropriate methods for communicating in an efficient manner and to make sure that the expectations of all stakeholders are set accordingly.