The rapid growth of mobile Internet use requires highly flexible and adaptable user interfaces for web applications. Contextual data from various sources as for example device HMI constraints, environmental information or device sensors need to be taken into account to dynamically adapt the application's UI. The same is true for web applications that are based on context defined service orchestration. To tackle the complexity of multiple, possibly interacting adaptations of web user interfaces, the authors propose the use of semantic user interface descriptions [1] and automatic creation of adapted user interface code via logic-based Conditional Transformations [7, 10] of UI representations. With our approach, existing representations of context values in logic databases [16], can easily be included into the adaptation.