We introduce a Janus-faced reference net component that presents the basis for the recursive composition of complex systems from open system units. We particularly focus on the operational aspect of relating different levels of action at different system levels.
We have presented various aspects of our organization-oriented software
engineering approach Sonar/Organ [
Organ rests on the universal model of an open and controlled system unit from Figure 1 that is applied at all system levels. We distinguish different internal system units (that are again instances of the universal model from Figure 1). Integration units together with operational units represent the “here and now” of the system unit in focus. The operational units are so to say the intrinsic units and carry out the system’s primary activities. They are dependent on the integration units which offer a technical frame via intermediary, regulation, and optimisation services in the course of integration processes. The governance units represent the “there and then” of the system unit in focus. They offer a strategic frame via goal/strategy setting, boundary management, and transmitting their decisions to the other internal system units in the course of governance processes.
Each system unit is a Janus-faced entity. It “looks inwards” by embedding other system units and at the same time “looks outwards” by being itself embedded in other system units. Thus, besides the already mentioned internal (technical and strategic) frames, each system unit in focus is externally framed by surrounding system units to which the system unit in focus relates via periphery processes. To conclude, we take a recursive, self-similar nesting approach, +
Peripheral Processes entry use frame leaving
+ Governance Integration
Operation +
Integration Processes
offer/use emergence technical disappearance frame
System Unit +
Governance Processes addition sotffrfreaatrme/ugesice removal
Operation: Primary activities Integration: Regulation, optimization Governance: Goal/strategy setting, planning,
boundary management Integration + Operation: "Here and now"
Governance: "Then and there"
borrowed from Koestler’s concept of a holon [
In our previous contributions we have stressed the underlying Petri net
semantics (specifically, reference net semantics [
Figure 2 displays a reference net component that reduces the various concepts from Figure 1 to internal system units, system processes and internal or peripheral actions of system units in the course of these processes. The component has the already mentioned Janus-faced character: It “looks inwards” by providing a platform for its embedded system units and at the same time “looks outwards” by being itself embedded inside other enclosing system units.
Each internal action takes place in the course of some system process (sp) and is carried out by some internal system unit (su). It carries an action identifier (actID) that is unique in the context of the associated process. The corresponding system unit is identified by its address (addr) and is passed the identifier of the process (pID) in whose course the action is carried out. Finally, each action is associated with some data (data).
Peripheral actions are also carried out by internal system units. However, from the perspective of surrounding system units, they are carried out by the system unit in focus as a whole. Thus, we arrive at a technical understanding of collective/corporate action. As an additional argument, peripheral actions are not only associated with an internal system process but also with the corresponding identifier of the system process of the surrounding system unit (pID2).
We first have a look at a simple production process in Figure 3 with only internal actions. It can be read according to the common UML understanding: Places and Transitions on a vertical line represent the life line of some role while places and transitions on a horizontal line represent a message exchange between different role players. As we do not look at process instantiation here, we assume that the process net exists permanently (on the place system processes) and may be used for multiple concrete production scenarios. System unit addresses are associated with process roles and product identifiers dynamically at the first transitions of the corresponding life lines. We now take a look at open systems by extending our modelling from the previous subsection with an additional system level that brings with it a collective level of action as can be seen in Figure 4. We have to decide, which are the atoms of our system, those parts from which all other activities eventually stem. These atoms are marked in Figure 4 as individuals. As they embed no internal system units themselves, they are not built according to the Janus-faced system unit from Figure 2.
We now have a look at how different levels of action interfere. As an example we take a look at the manager from the production firm that acts in turn on the market. Figure 5 displays how actions of the manager either only take place on the level of the firm or are additionally transformed to collective level actions of the firm itself on the market. – Step 1: The manager accepts a product order that occurs on the market.
The manager accepts on behalf of the firm. Consequently, it acts on two system levels simultaneously: (1) at the firm level where a new production activity is initiated and (2) at the market level where the manager’s action is transformed into a collective level action of the firm. – Steps 2 + 3: The simple production scenario from Figure 3 can be found (slightly modified) as a substructure of the system process at the firm level in Figure 5. It still contains only (firm-)internal actions and in steps 2 and 3 the manager delegates the market order to some producer of the firm and afterwards receives the finished product. – Step 4: The manager ships the finished product to the customer on the market. Just like in step 1, the manager acts both on the firm level (itself) and on the market level (its action transformed into a collective level one on behalf of the firm). 4
We have presented a reference net operationalisation for combining different levels of action in complex systems that are hierarchically built up from open system units. This addresses one particular aspect of our previously published Organ-model for building software systems in the large as systems of systems.
Our operational approach rests on a generic Janus-faced net component that allows to recursively nest system levels inside each other. The generic interface of the component allows to regard each system unit without the need to bother with internal details of lower-level system units. For instance, in the example from Figure 5 it would easily be possible to expand the manager part into a complex system unit containing multiple managers (e.g. a salesman for market exchange management and a foreman for internal production management). This move would have no effect on the current process definition at the firm level. Consequently, our approach allows for the modular prototyping of hierarchically organized systems of systems that are composed of open system units.