16
2 Simulation-Based Optimization
the activity-oriented and the transaction-oriented view find little or no practical
relevance anymore [Pa1991, pp. 25 and 29]. The process interaction view summarizes logically connected activities which occur in defined pattern to processes
through which the entities in a model flow. The interactions in a model are thus
not described by events but through processes [PO1999, p. 26]. A sub-class of the
process interaction approach is the transaction flow, which differentiates transactions (dynamic objects) and stationary objects (stations). While the event-oriented
worldview was basically used during the first two decades of simulation, focusing
on the events themselves as the main modeling event, the process-oriented world
view provides a more natural way to describe a system which is easier to model
[Pe2017, pp. 83–84]. The event-discrete time advance is also used for agent-based
simulation (ABS) models [NM2007, p. 11].
In the 1980s, the process-oriented view gradually replaced the event-oriented
world view, therefore most DES systems are process-oriented by default. Nevertheless, the event-oriented time progress forms the core of most discrete-event
simulators [KSZ2002, p. 37]. “All discrete event simulation systems implement
their internal logic using this basic modelling approach, regardless of the world
view that they present to the user” [Pe2010a, p. 212]. The process-oriented worldview is nowadays often implied when the term DES is used. This assumption also
applies for this work.
The simulation concepts used in this work are based on the classification
described above. For completeness, it should be mentioned at this point that
other classification options for simulation models can be found, in Law and
Kelton [LK2000], Banks et. al [Ba+2005], and Wenzel [We2000]. Zeigler,
Praehofer and Kim describe different modeling formalisms according to the
presentation of the time base and the value of state variables. They describe
three different basic formalisms 6 , the Differential Equation System Specifications (DESS), the Discrete Time System Specifications (DTSS) and the Discrete
Event System Specifications (DEVS) [ZPK2010, p. 6, p. 137 ff.]. The interested
reader is referred to the further literature, since in-depth explanations would go
beyond the scope of this work.
6 Besides the three basic formalisms DESS, DTSS and DEVS and for the sake of completeness,
the Discrete Dynamic Systems has to be mentioned as well as a specification of the DEVS
models. The interested reader is referred to the detailed explanations in [ZPK2010, p. 6 and
p. 137 ff.].
2 Simulation-Based Optimization
the activity-oriented and the transaction-oriented view find little or no practical
relevance anymore [Pa1991, pp. 25 and 29]. The process interaction view summarizes logically connected activities which occur in defined pattern to processes
through which the entities in a model flow. The interactions in a model are thus
not described by events but through processes [PO1999, p. 26]. A sub-class of the
process interaction approach is the transaction flow, which differentiates transactions (dynamic objects) and stationary objects (stations). While the event-oriented
worldview was basically used during the first two decades of simulation, focusing
on the events themselves as the main modeling event, the process-oriented world
view provides a more natural way to describe a system which is easier to model
[Pe2017, pp. 83–84]. The event-discrete time advance is also used for agent-based
simulation (ABS) models [NM2007, p. 11].
In the 1980s, the process-oriented view gradually replaced the event-oriented
world view, therefore most DES systems are process-oriented by default. Nevertheless, the event-oriented time progress forms the core of most discrete-event
simulators [KSZ2002, p. 37]. “All discrete event simulation systems implement
their internal logic using this basic modelling approach, regardless of the world
view that they present to the user” [Pe2010a, p. 212]. The process-oriented worldview is nowadays often implied when the term DES is used. This assumption also
applies for this work.
The simulation concepts used in this work are based on the classification
described above. For completeness, it should be mentioned at this point that
other classification options for simulation models can be found, in Law and
Kelton [LK2000], Banks et. al [Ba+2005], and Wenzel [We2000]. Zeigler,
Praehofer and Kim describe different modeling formalisms according to the
presentation of the time base and the value of state variables. They describe
three different basic formalisms 6 , the Differential Equation System Specifications (DESS), the Discrete Time System Specifications (DTSS) and the Discrete
Event System Specifications (DEVS) [ZPK2010, p. 6, p. 137 ff.]. The interested
reader is referred to the further literature, since in-depth explanations would go
beyond the scope of this work.
6 Besides the three basic formalisms DESS, DTSS and DEVS and for the sake of completeness,
the Discrete Dynamic Systems has to be mentioned as well as a specification of the DEVS
models. The interested reader is referred to the detailed explanations in [ZPK2010, p. 6 and
p. 137 ff.].