The abstract concepts and the complex methods can usually be easier understood if some grapho-analitical techniques are used. The Real-Time Systems (RTSs) include a wide variety of concepts such as concurrency, parallelism and synchronization, or methods for specification, design, verification, implementation etc. that have to be connected together. For this aim the using of Petri nets is proposed in the paper as a link between graphical representation and analytical methods, in order to give some tools for achieving the software life cycle.