Glossary clarifications for "simulator - simulation program - simulation tool"

[chrbertsch]

We were contacted by a user via contact@fmi-standard.org with the following question:

"... The following terms are defined in the glossary:
simulation program: Software to develop and/or solve simulation models. The software includes a solver, may include a user interface and methods for post processing (see also: simulation tool, simulation environment).
simulator: A simulator can include one or more simulation programs.
I am confused about this because the two terms are sometimes used interchangeably in the specifications. This can also be seen in the definition of co-simulation in the FMI-specification, which is defined via simulation tools but referred to synonymously with simulator coupling:
Co-simulation: Coupling of several simulation programs in order to compute the global behaviour of a system that consists of several subsystems. The subsystems are coupled in the sense that the behaviour of each subsystem depends on the behaviour of the remaining subsystems, so that the co-simulation must be computed in a step-by-step fashion. Each simulation program is responsible for computing the behaviour of a subsystem, using the outputs produced by the other simulation programs. Synonyms: dynamic mutual-exchange, simulator coupling, and coupled simulation.
Without demanding a universal definition, as a newcomer to the field I would be interested in the difference between simulator and simulation tool. If possible, an example would be helpful. Referring to [Palensky 2017]1 (simulator) or [Gomes 2018]2 (simulation unit) consists of the model and the solver. Intuitively, I would equate "simulation tool" with "simulator" according to the above definition."

While I do not fully understand the problem described above, I think there are some things to clarify

• we should distinguish between "Co-simulation" and "simulator-coupling"/"tool coupling". To my understanding, simulator-/tool-coupling is a special form of co-simulation, where the original simulation tools ("simulators") and are involved (typically also with their GUI), while ca co-simulation could also be done using CS FMUs that had been exported from the original simulations tools.
• "simulation program" is not used outside the glossary, and it is defined as a synonym to "simulation tool". Do we need this definition at all?
• I do not see the difference between "simulation tool" and "simulator" and would use them as synonyms. What would be a simulator, that includes several simulation programs? (A co-simulation platforms such as Model.Connect? Then we need to define this)