Abstract: The invention relates to a mechanism for detecting forks within data flow diagrams corresponding to application programs and for controlling the execution of such application programs. The flow diagram is preferably formed by interconnecting a plurality of symbolic representations of program objects with a plurality of wire constructs. The symbolic representations correspond to program objects having input properties and configured to execute pre-defined functions based on the values of its input properties. The flow diagram preferably represents a logical flow of information used to set the input property values of the program objects. According to the invention, the input properties of the program objects are first invalidated. Next, information is allowed to flow along at least a portion of the diagram, thereby setting one or more of the program objects' input property values. In response to having its input property value set, the program object validates the respective input property.