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The importance of context dependent modelling of complex systems, depending on the observer's point of view will be discussed. Thus, context is synonymous for the content of a problem in a frame of the goals, starting points and ways to achieve these aims. In this light, difficulties of model validation and a general method how to overcome them was discussed. The relations among subject – object – model in the light of a systems approach; Charles Sanders Peirce's triad principle and the semiotic principle of communication was presented.

The appropriateness of a system dynamics methodology, which is due to its transparency and clarity an excellent tool for modelling of complex systems.

In the paper the equivalence of different methodologies was shown, whose differences and similarities can be judged only in context of a problem and the aims of researches. For illustration, the methodology is applied to a tourism system, which possesses the typical properties of global and local organisations. A verbal description of a tourism problem is followed by a causal loop diagram, which helps to discuss the problem categorically.

As the methodology is implemented using quantitative model and POWERSIM tools; it offers the solution of national tourism strategy implication, selected from different scenarios.

This paper presents a simulation model of the tourism in a frame of system dynamics, developed from qualitative models, as an illustration of the discussed methodology.

This paper aims to describe the development and application of a manpower planning system for the Slovenian armed forces using a system approach, system dynamics (SD) and numerical optimization.

The model of the hierarchical manpower system was developed by SD methodology and formulated in discrete time space. The problem of tracking the goal trajectories in the eight topmost ranks at the prescribed boundaries was solved by application of the quadratic performance index and finite automata (FA) which was used for classification of acceptable strategies. Genetic algorithms (GA) as well as pattern search were compared at the numeric optimization.

Employing SD and a system approach increases the understanding of the system control. The definition of an optimum strategy, which would consider only target values for ranks within prescribed parameter boundaries, could provide an undesired oscillatory solution. Inclusion of rules by FA to determine acceptable strategies based on the time response of a strategy provided acceptable, nonoscillatory solutions. GA and pattern search were considered where pattern search was shown to be significantly more suitable for the task of control strategy determination.

The developed system and methodology was applied by the Slovenian Armed Forces in the process of restructuring.

The developed approach permits a moderate transition to the new desired structure. Restructuring without a clear understanding of the system structure and dynamics might result in undesired social impacts such as strikes and riots.

Provision of the systemic view of the hierarchical manpower system and application of FA to determine the proper control of a complex system.