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Adaptation
An application generated from an SDL description can be viewed as having three parts:
- The SDL system
- The physical environment of the system
- The environment functions, where the SDL system is connected with the environment
When adapting the application, the environment functions may have to be specified depending on the integration mechanism used. The environment functions are the place where the two worlds, the SDL system and the physical environment, meet. Signals sent from the SDL system to the environment can be specified to perform any event in the physical environment, and events in the environment are specified to cause signals to be sent into the SDL system.
In a distributed system an application might consist of several communicating SDL systems. Each SDL system will become one executable program. The environment functions that has to be written for each SDL system are:
- xInitEnv - handles the initialization of the environment and will be called during the start-up of the application (before the SDL system is initialized).
- xCloseEnv - is called when the SDL system terminates.
- xOutEnv - will be called each time a signal is sent out of the SDL system.
- xInEnv - This function is repeatedly called during the execution of the system. During this call, the environment could be scanned for events which should result in a signal sending into the SDL system.
- xGlobalNodeNumber - returns a number that is unique for each communicating SDL system that constitutes an application.
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