When building process-intensive web applications, developers typically spend considerable effort on the exchange of specific data entities between specific web pages and operations under specific condi-
tions, as called for by business requirements. Since the WWW infrastructure provides only very coarse data exchange mechanisms, we introduce a notation for the design of fine-grained conditional data flows between user interface components. These specifications can be interpreted by a data flow controller that automatically provides the data entities to the specified receivers at run-time, relieving developers of the need to implement user interface data flows manually