Declarative User Interfaces : specifying UI variabilities

In our research we apply the principle of separation of concerns onto User Interfaces. The goal is to get a clean separation in the source code between code responsible for UI logic and code responsible for the application logic. Since both are tightly coupled (i.e. the application logic needs to interact closely with UI logic and vice versa), this results in code entanglement which reduces the evolvability of the software. Therefore it is difficult to vary the way a user interface is layed out (e.g. using a tabbed, multi-column, or multi-windows strategy) or how it should be handled on different platforms (e.g. PDA , internet based). In our approach we use SOUL, a declarative meta programming environment, to describe the different UI concerns. This declarative specification is taken as input by our SoGUI reasoner, that transforms it into a working user interface (where application logic and UI logic are once again woven together). This way it is possible to vary the UI visualisation and behaviour by merely changing the declarative specifications (facts and rules) that describe these UI concerns. Each variability is captured by a set of rules. The reasoning mechanism combines the different sets to generate the UI variant emerging from the chosen variabilities. For specifying the UI we anticipate the use of visual tools. Once the UI is modelled visually, the tool translates the specification into a declarative specification for this is the base modelling language in our approach. Next the reasoning mechanism transforms this model into the actual working UI (i.e. the actual code).