Integration of GEM and SOTA.
2.1.1 From SOTA to GEM SOTA (State Of The Affairs) [ABZ12] is the ASCENS approach to describing the overall domain and the requirements for a system. SOTA abstracts the behavior of a system with a single trajectory through a state space. The state space is the so called state-of-the-affair space, and it represents the set of all possible states of the system at a single point of time (see Figure 3). ⟨ ⟩ The requirements of a system in SOTA are expressed as goals. A goal is an area of the SOTA space that a system should eventually reach, and it can be characterized by a goal pre-condition (the area of the SOTA space which activates the need of achieving a goal), the post-condition (the goal in itself, that is the actual area which has to be eventually reached for the goal to be satisfied), and utilities (constraints on how the goal should be reached, i.e., along which trajectory). Formally: G = Gpre, Gpost , U . SOTA is concerned with the overall domain and the requirements of the system. For this it is sufficient to deal with the state of the affairs without regard for details such as the state’s internal structure or the probabilities of the different trajectories. However, for a more detailed investigation of the structure and behavior of ensembles, we need a more expressive model. To this end, the concepts underlying General Ensemble Model (GEM) defined in WP1 (early described [HW11]) to model the behavior of ensembles, has been re-formulated in terms of an extension and generalization of SOTA. As in SOTA, in GEM it is not necessary to distinguish between ensemble and environment. How- ever, whenever it is necessary to do that, or when the system specification enforces such a distinction, a unique state space can always be obtained by combining ensemble and environment using a so-called Figure 3: The trajectory of an entity in the SOTA space, starting from a goal precondition and trying to reach the postcondition while moving in the area specified by the maintain condition. combination operator; in general, we will use the term system to refer to this combination. Combina- tion operators are also used as the means to hierarchically build ensembles from simpler components and smaller ensembles; therefore they serve as a uniform way to model a system’s structure and be- havior. ⊆ In general, a system can behave in a non-deterministic manner and therefore have multiple possible trajectories through the state space. In GEM we identify a system S with the...
