A system and method may generate executable block diagrams in which at least some of the blocks run in accordance with message-based execution semantics. A message may include an input data payload that does not change over time, and the message may persist for only a determined time interval during execution of block diagram. A message-based execution engine may control execution of message-based blocks in which a source block may generate a message at a particular point in time, the message may be sent to one or more destination blocks triggering execution of those blocks, and the message may be destroyed on or after a determined time interval. Other execution domains, such as a time-based or state-based execution domain, may be provided, and the system may implement a hybrid execution model.