A method for operating a computer system to modify a graph at runtime, the graph being used to generate executable instructions when the graph is executed, the graph including vertices representing components with parameters and links between components indicating flows of data between the components, each of the components including a data file or providing a process to be executed, the computer system including a repository that stores the components, the method including using the computer system to perform: (a) after having determined at least one runtime parameter associated with the graph, determining at runtime whether any component of the graph is defined as being a conditional component based on whether parameters associated with the component include a condition and a condition-interpretation, the condition-interpretation having two allowed mutually exclusive values for interpreting how the graph is modified when the condition is met, the value of the condition-interpretation being previously determined; (b) evaluating the condition for every such conditional component based on the at least one runtime parameter; and; (c) modifying the graph at runtime in accordance with such evaluation and the corresponding condition-interpretation of such conditional component including, if the condition is not met the component is not removed from the graph before execution else removing (1204, 1206) the conditional component, all connected flows to such conditional component, and each component and flows connected to such components that depend on the presence of the conditional component from the graph before execution of the graph based on a first allowed value of the condition-interpretation for such conditional component, or replacing the conditional component with a flow before execution of the graph based on a second allowed value of the condition-interpretation for such conditional component. (a) after having determined at least one runtime parameter associated with the graph, determining at runtime whether any component of the graph is defined as being a conditional component based on whether parameters associated with the component include a condition and a condition-interpretation, the condition-interpretation having two allowed mutually exclusive values for interpreting how the graph is modified when the condition is met, the value of the condition-interpretation being previously determined; (b) evaluating the condition for every such conditional component based on the at least one runtime parameter; and; (c) modifying the graph at runtime in accordance with such evaluation and the corresponding condition-interpretation of such conditional component including, if the condition is not met the component is not removed from the graph before execution else removing (1204, 1206) the conditional component, all connected flows to such conditional component, and each component and flows connected to such components that depend on the presence of the conditional component from the graph before execution of the graph based on a first allowed value of the condition-interpretation for such conditional component, or replacing the conditional component with a flow before execution of the graph based on a second allowed value of the condition-interpretation for such conditional component.