Comparing Discrete Event and Agent Based Simulation in Modelling Human Behaviour at Airport Check-in Counter Mazlina Abdul Majida, Uwe Aickelinb, Peer-Olaf Sibersb, mazlina@ump.edu.mya, uxa@cs.nott,ac,uk, pos@cs.nott.ac.uk a Dr, Faculty of Computer Systems & Software Engineering, Universiti Malaysia Pahang, Lebuhraya Tun Razak, Kuantan, 26300, Malaysia Elsevier use only: Received date here; revised date here; accepted date here Abstract Simulation is a well-established what-if scenario analysis tool in Operational Research (OR). Discrete Event Simulation (DES) and System Dynamics Simulation (SDS) are the predominant simulation techniques in OR. However, a new simulation technique, namely Agent-Based Simulation (ABS) is gaining more attention in modelling human behaviour. In our research we focus on modelling human behaviour using DES and combined DES/ABS. The contribution made by this paper is the comparison of DES and combined DES/ABS for modelling human reactive and different level of detail of human proactive behaviour in service systems e.g. check-in services in an airport. The results of our experiments show that the level of proactiveness considered in the combined DES/ABS model has a big impact on the simulation outputs. Therefore, for service systems of the type we investigated we would suggest to use combined DES/ABS as the preferred analysis tool. © 2001 Elsevier Science. All rights reserved Research Highlights We compare DES against combined DES/ABS in modelling human behaviour We model human reactive and proactive behaviours in an airport check-in counter Modelling human behaviours as actual as possible in DES/ABS model shows a significant impact on the outputs Significant to model human behaviour realistically on a queuing service system Keywords : Simulation,;Discrete Event Simulation,;Agent Based Simulation; Reactive Behaviour;Proactive Behaviour 1. Introduction Simulation has become a preferred tool in Operation Research for modelling complex systems (Kelton et al. 2007). Simulation is considered a decision support tool which has provided solutions to problems in industry since the early 1960s (Shannon 1975). Studies in human behaviour modelling and simulation have received increased focus and attention from simulation research in the UK (Robinson, 2004). Human behaviour modelling and simulation refers to computer-based models that imitate either the behaviour of a single human or the collective actions of a team of humans (Pew and Mavor 1998). Discrete Event Simulation (DES) and Agent Based Simulation (ABS) are simulation approaches often used for modelling human behaviour in Operational Research (OR). Examples can be found in Brailsford et al. (2006) and Siebers et al (2010). The capability of modelling human behaviour in both simulation approaches is due to their ability to model heterogeneous entities with individual behaviour. Another simulation approach commonly used in OR is System Dynamic (SD). However, this approach focuses on modelling at an aggregate level and is therefore not well suited to model a heterogeneous population at an individual level. Because of this limitation, SDS is not considered in the present study. Human behaviour can be categorised into different types, many of which can be found in the service sector. When talking about different kinds of human behaviour we refer to reactive and 2 Submitted to Elsevier Science proactive behaviour. Here, reactive behaviour is related to staff responses to the customer when being requested and available while proactive behaviour relates to a staff member’s personal initiative to identify and solve an issue. When providing services proactivity of staff plays an important role in an organisation's ability to generate income and revenue (Rank et al, 2007). But the question here- is it useful to consider proactive behaviour in models of service systems and which simulation techniques is the best choice for modelling such behaviour? Thus, in this paper we investigate the impact of modelling different levels of proactive behaviour in DES and combined DES/ABS. We compare both simulation techniques in term of simulation result using a real world case study: check-in services in the airport. Previously we have studied the capabilities of DES and combined DES/ABS in representing the impact of reactive staff behaviour (Majid et al, 2009) and mixed reactive and proactive behaviour in a retail sector (Majid et al, 2010) and public sector (Majid et al, 2012). In this paper we look at the capabilities of DES and combined DES/ABS in representing the impact of mixed reactive and proactive behaviour on another complex public sector system. The paper is structured as follows: In Section 2 we explore the characteristics of DES and ABS and discuss the existing literature on modelling human behaviour in service sector. In Section 3 we describe our case study and the simulation models development and implementation. In Section 4 we present our experimental setup, the results of our experiments, and a discussion of these results. Finally, in Section 5 we draw some conclusions and summarise our current progress. 2 Literature Review 2.1 Human Behaviour Modelling in DES and ABS This chapter reviews existing research studies on modelling human behaviour using DES and ABS techniques. As explained by Pew and Mavor (1998), Human Behaviour Representation (HBR), also known as human behaviour modelling, refers to computer-based models which imitate either the behaviour of a single person or the collective actions of a team of people. Nowadays, research into human behaviour modelling is well documented globally and discussed in a variety of application areas. Simulation appears to be the preferred choice as a modelling and simulating tool for investigating human behaviour (ProModel 2010). This is because the diversity of human behaviours is more accurately depicted by the use of simulation (ProModel 2010). Throughout the literature, the best-known simulation techniques for modelling and simulating human behaviour are DES and ABS. Among existing studies on modelling human behaviour, the use of DES is presented by Brailsford et al. (2006), Nehme et al. (2008) and Baysan et al.(2009). On the other hand, Schenk et al. (2007), Siebers et al. (2007) and Korhonen et al. (2008a; 2008b) recommend ABS for modelling human behaviour. Brailsford et al. (2006) claim that, based on their experiments of modelling the emergency evacuation of a public building, it is possible to model human movement patterns in DES. However, the complex nature of DES structures where entities in the DES model are not independent and self-directed makes the DES model inappropriate for modelling largescale systems. This characteristic of entities in DES is agreed by Baysan et al.(2009), who have used DES in planning the pedestrian movements of the visitor to the Istanbul Technical University Science Center. However, due to the dependent entities in the DES model, the pedestrian movement pattern in their simulation model is restricted to pre-determined routes. By contrast, Korhonen (2008a; 2008b) has developed an agent-based fire evacuation model which models people-flow in free movement patterns. He states that the decision to use ABS is due to the fact that agent-based models can provide a realistic representation of the human body with the help of autonomous agents. In addition to modelling human behaviour using DES, Nehme et al (2008) have investigated methods of estimating the impact of imperfect situational awareness of military vehicle operators. They claim that it is possible to use the DES model to understand human behaviour by matching the results from the DES model with human subjects. Schenk et al. (2007) comment that modelling consumer behaviour when grocery shopping is easier using ABS because this model has the ability to integrate communication among individuals or consumers. Siebers et al. (2007) assert that their research in applying ABS to simulate management practices in a department store appears to be the first research study of its kind. They argue that ABS is more suitable than DES due to the characteristics of the ABS model; specifically, it allows to model proactive and autonomous entities Submitted to Elsevier Science that can behave similar to humans in a real world system. Instead of choosing only one simulation technique to model human behaviour, some researchers tend to combine DES and ABS in order to model a system which cannot be modelled by either method independently. Examples are Page et al. (1999) who studied the operation of courier services in logistics, Kadar et al. (2005) who investigated manufacturing systems, Dubiel and Tsimhoni (2005) who studied human travel systems and Robinson (2010) who looked at the operation of coffee shop services. They all agree that DES and ABS modelling can complement each other in achieving their objectives. A combination of ABS and DES modelling is useful when human behaviour has to be modelled for representing communication and autonomous decision-making. In conclusion, the research into human behaviour using DES and ABS that has been carried out so far suggests that DES and ABS are able to model human behaviour but take different approaches (dependent entities vs. independent agents). The studies outlined above indicate that DES is suitable for capturing simple human behaviour, but is problematic when applied to more complex behaviours as the next event to occur in DES has to be determined. In contrast, ABS offers straightforward solutions to modelling complex human behaviour, i.e. free movement patterns or employee proactive behaviour, as agents can initiate an event themselves. However, for ABS the resource requirements (computational power) are much higher and the modelling and implementation of the model is more complex. 2.2 The Simulation Choice For our comparison exercise we have chosen to use DES and combined DES/ABS. As we are interested to investigate a service oriented system in the public sector, which involves queuing for the different services we cannot use pure ABS for our investigations, as in pure ABS models the system itself is not explicitly modelled but emerges from the interaction of the many individual entities that make up the system. However, as ABS seems to be a good concept for representing human behaviour we use a combined DES/ABS approach where we model the system in a process-oriented manner while we models the actors inside the system (the people) as agents. 3 3 Case Study Description The operation at the check-in counters in an airport has been chosen as third case study (first case study-Majid, 2010 and second case study - Majid, 2012) because it demonstrates a diversity of contact between counter staff and travellers, which is essential to this study of human behaviour. Information on this third case study is chosen from “Simulation with Arena” by Kelton (2007). Figure 1 illustrates the operation at the airport check-in service, the numbering and red arrows representing the sequence of operation. The operation at the airport check-in service of this case study starts from the point at which travellers enter the main entrance door of the airport and progress to the one from the five check-in counters of an airline company (represented by arrow number 1 in Figure 1). The operation at the five check-in counters is from 8.00 am to 12.00 am every day. If members of staff at the related check-in counters are busy, the travellers have to wait in the counter queue (represented by arrow number 2 in Figure 1). If counter staff are available, then travellers will move to the check-in counter (represented by arrow number 3 in Figure 1). Once their check-in is completed, the travellers are free to go to their boarding gates (represented by arrow number 3 in Figure 1). To model the human reactive and proactive behaviours, information on real human behaviours at the airport is gathered through secondary data sources such as books and academic papers. The reactive behaviour that has been investigated relates to counter staff reactions to travellers in processing their check-in requests and their response to travellers waiting in queues during busy periods. The proactive behaviours have been modelled are the behaviours of another member of staff (supervisor) who is responsible for observing and controlling the checkin services. The first proactive behaviour of a supervisor is a request to the counter staff to work faster in order to reduce the number of travellers waiting in queues. The decision to execute such proactive behaviour is based on their working experience. Identifying and removing any suspicious travellers from queues is the supervisor’s second proactive behaviour to be modelled, their decision again based on observation and working experience. Suspicious travellers include those with overweight hand or cabin luggage, drunken travellers and 4 Submitted to Elsevier Science unauthorised pregnant women. The proactive behaviour of travellers is related to their search for the shortest queue in order to be served more quickly. The decision by travellers to execute such proactive behaviour is generated from knowledge that they gather through observing other queues while checking-in. After analysing the operation at the check-in counter, the level of detail to be modelled in the DES and combined DES/ABS models, also known conceptual modelling, is then considered. Both, the DES model and the combined DES/ABS model are based on the same conceptual model (Figure 2) but the strategy of implementation in both cases is very different. DES modelling uses a process-oriented approach, i.e. the development begins by modelling the basic process flow of the check-in services operations as a queuing system. Then, the investigated human behaviours, reactive and proactive are added to the basic process flow (Figure 2). Two different implementation approaches are used for developing the combined DES/ABS model: the process-oriented Travellers travel to boarding gate Travellers travel to boarding gate 3 Counter 1 3 Boarding gates Counter 2 Counter 3 Counter 4 Counter 5 Travellers being serve by counter staffs 2 2 2 2 Travellers in queues 2 Observing supervisor 1 1 1 1 1 Arriving travellers Main Entrance Figure 1: The illustration of the check-in services in an airport 4 Simulation Models 5 Submitted to Elsevier Science Queuing system and Human Behaviours in DES Model Start Reactive behaviour Travellers arrive at the airport’s main entrance Travel to the check-in counters Counter staffs busy? Counter staff processes checkin request by travellers No Travellers travel to the boarding gate End Yes A2 Proactive behaviour Travellers queuing Proactive behaviour Supervisor managing the check-in area A1 Proactive behaviour A B Travellers’ proactive behaviours Supervisor’s proactive behaviours Jump queue while queuing to the shortest queue Proactive B2 Request counter staff that has long queue to work faster Removing the suspicious travellers from queueing Figure 2 : The implementation of DES model Individual Behaviour by ABS Model Travellers State Chart Diagram counter staff available waiting to be served being served travel to check-in counter being idle idle serving travellers Supervisor State Chart Diagram observing Message passing finish serving travellers busy travellers enter the airport’s main entrance Message passing Counter Staff State Chart Diagram Message passing travellers leave to boarding gate Message passing Jump queue upon arrival to the shortest queue Proactive B1 Proactive A2 Message passing Proactive A1 B2 send message to counter staff return to observe busy Figure 3: The implementation of combined DES/ABS model Proactive behaviour B1 6 Submitted to Elsevier Science approach is used for the DES modelling (Figure 2) and the individual-centric approach is used to model the agents. Figure 3 shows some state charts that represent the different types of agents in the model (travellers, counter staff and supervisor). Table 2 : Counter staff service time Service Time Parameters Value Counter staff service time Weibull (7.78,3.91) Two simulation models have been developed from the conceptual models and have been implemented in the multi-paradigm simulation software AnyLogic™ (XJTechnologies, 2013). Both simulation models consist of one arrival process (travellers), five single queues, and resources (five counters staff). Travellers, counter staff and supervisor are all passive objects in the DES model while in the combined DES/ABS all of them are active objects. Passive objects are entities that are affected by the simulation‘s elements as they move through the system, while active objects are entities acting themselves by initiating actions (Siebers et al., 2010). iii. A discussion follows on how objects in DES model or agents in combined DES/ABS model are set up: i. Travellers object/agent The arrival rate of the simulation model is gathered from “Simulation with Arena” by Kelton (2007). In both DES and combined DES/ABS models, the arrival process is modelled using an exponential distribution with the arrival rate shown in Table 1. The arrival rate is equivalent to an exponentially distributed inter-arrival time with mean = 1/rate. The travel time as stated in Table 1 is the delay time for travellers moving from the airport entrance to the check-in counters. Table 1 : Travellers arrival rates Arrival Type Time Rate Travellers arrival 8.00 – Approximately 30 time 24.00 am people per hour Travellers travel upon Uniform (1,2)time arriving minimum 1 minute , maximum 2 minutes ii. Counter staff object/Agent In both simulation models, five members of counter staff have been modelled performing the task of processing travellers’ check-in requests. Task priority is allocated on a first in first out basis according to the service time stated in Table 2 below: Supervisor Agent (only in combined DES/ABS model) The supervisor agent is modelled in the combined DES/ABS model while in DES model the supervisor is imitated by a set of selection rules (programming function). This is because in the DES model the communication between the entities is not capable of being modelled. In both simulation models, the supervisor is not directly involved with the checkin process. He/she is there only to observe the situation at the check-in counter, so no service time is defined for the supervisor for both simulation models (DES and combined DES/ABS). We conducted 100 replications for each set of parameters. Both simulation models use the same model input parameter values. Therefore, if we see any differences in the model outputs they will be due to the impact of the differences between the modelling techniques. The run length for this case study is 16 hours, imitating the normal operation of the check-in counter at an airport. The verification and validation process are performed simultaneously with the development of the basic simulation models (DES and combined DES/ABS). 5 Experiment and Results The purpose of the experiment is to compare the simulation results between DES and combined DES/ABS models when modelling human reactive and proactive behaviours. The experiment sought to find out what could be learnt from the simulation results when modelling complex proactive behaviours for the realistic representation of the real– life system using two different simulation techniques. The comparison of simulation results for DES and combined DES/ABS models is conducted statistically by performing a T-test. For our comparison we use the following hypotheses: Ho1 : Modelling human reactive behaviour in DES model produce statistically the same simulation results with combined DES/ABS model 7 Submitted to Elsevier Science Ho2 : Modelling human mixed reactive and proactive behaviour in DES model produce statistically the same simulation results with combined DES/ABS model Four simulation models have been developed: 1. Reactive DES model 2. Reactive Combined DES/ABS model 3. Mixed Reactive and Proactive DES model and 4. Mixed Reactive and Proactive DES/ABS models. Two types of experiments have been conducted as shown in Table 3. Table 3: Experiment Description Experiment Description Experiment 1 Experiment 2 Reactive DES versus Reactive Combined DES/ABS Mixed Reactive and Proactive DES versus Mixed Reactive and Proactive DES/ABS In this experiment, the general idea of reactive (response to environment) and proactive behaviours as described in section 4 were imitated and modelled. The first proactive behaviour that was modelled in this experiment is related to the behaviour of the supervisor, who is responsible for ensuring that the check-in process is under control. The supervisor’s proactive behaviour is demonstrated by requesting counter staff to work faster in order to serve travellers who have been waiting a long time. The decision of requesting counter staff to work faster is based on the supervisor’s awareness that some travellers would not move to another shorter queue. The second proactive behaviour is demonstrated by the behaviours of travellers who require faster service. Finding the shortest queue on arrival at the check-in services and moving from one queue to another shorter queue while queuing have exemplifies the proactive behaviours of travellers. Finally, the third proactive behaviour is exhibited in identifying suspicious travellers by the supervisor, based on their own experience and observation at the check-in counters To investigate the impact of modelling variation of proactive behaviours against reactive behaviours in DES and combined DES/ABS models, “customer waiting time” and “number of customers served” were used as our main performance measures. We have selected these measures as the literature recommends them as important measures to increase productivity in the service-oriented systems (Robert and Peter, 2004). In addition, we have used “counter staff utilisation” and “number of customers not served” as the additional performance measures. To execute the Experiment 2, the additional performance measures were used based on the investigated proactive behaviours (number of requests to work faster, number of travellers searching for shortest queue (upon arriving), number of travellers searching for shortest queue (while queuing) and number of travellers moved to the office). It is assumed that investigating these measures will provide sufficient evidence in understanding the impact of the simulation outputs for different behaviours in one simulation technique. The sub-hypotheses were built for each performance measure in DES and combined DES/ABS according to the list of experiments to be compared. Finally, the results of the performance measures in the Experiment 1 and 2 were gathered and compared for both simulation models (Table 4). The hypotheses for Experiment 1 are: Ho1_1 : Ho1_2 : Ho1_3 : Ho1_4 : The travellers waiting time resulting from the reactive DES model is not significantly different from the reactive combined DES/ABS model. The number of travellers served resulting from the reactive DES model is not significantly different from the reactive combined DES/ABS model. The counter staff utilisation resulting from the reactive DES model is not significantly different from the combined reactive DES/ABS model. The number of travellers not served resulting from the reactive DES model is not significantly different from the reactive combined DES/ABS model. The hypotheses for T-test in Experiment 2 are the same with the four hypotheses in Experiment A1 but these hypotheses are tested with a name link to Experiment 2 as follows: Ho2_1, Ho2_2, Ho2_3, and Ho2_4, for the travellers waiting time, the counter staff utilisation, the number of travellers not served and the number of travellers served, respectively. To complete the Experiment 2, the following additional sub-hypotheses are needed: Ho2_5 : The number of requests to work faster resulting from the mixed reactive and proactive DES model is not significantly different from the mixed reactive and proactive combined 8 Submitted to Elsevier Science Ho2_6 : Ho2_7 : Ho2_8 : hypotheses are failed to be rejected. Results in this case study have revealed a similar impact on both simulation models when modelling similar reactive behaviour. Hence, the simulation result for the reactive DES and combined DES/ABS models is statistically show no differences and the Ho1 hypothesis is failed to be rejected. Similarities and dissimilarities of results between DES and combined DES/ABS were found in this combined-proactive experiment, as shown in Table 4. Significantly, the combined DES/ABS model has produced a shorter waiting time, a lower number of requests to work faster and a higher number of travellers searching for the shortest queue while queuing compared to the DES model. This impact is significant, probably due to the extra individual DES/ABS model. The number of travellers searching for the shortest queue (upon arrival) resulting from the mixed reactive and proactive DES model is not significantly different from the mixed reactive and proactive combined DES/ABS model. The number of travellers searching for the shortest queue (while queuing) resulting from the mixed reactive and proactive DES model is not significantly different from the mixed reactive and proactive combined DES/ABS model. The number of travellers moved to the office resulting from the mixed reactive and proactive DES model is not significantly different from the mixed reactive and proactive combined DES/ABS model. Table 4 : Results of Experiment 1 and Experiment 2 Experiment 1 Experiment 2 DES Combined DES/ABS DES Combined DES/ABS 18.46 24.84 65 20.59 473 22.81 4 4.71 - 6.44 10.18 69 18.21 462 24.19 0 0 1 1.25 3.12 8.17 70 18.7 459 25.1 0 0 0 0.19 Mean 18.64 23.91 64 18.58 473 22.35 4 2.25 - SD - - 477 25.18 478 50.89 Number of travellers searching for the shortest queue (while queuing) (people) Mean - - n/a 223 - - Number of travellers moved to the office (people) Mean - - SD - - Performance measures Travellers waiting times (minute) Counter staff utilisation (%) Number of travellers served (people) Number of travellers not served (people) Number of requests to work faster Number of travellers searching for the shortest queue (upon arriving) (people) Mean SD Mean SD Mean SD Mean SD Mean SD SD Results for the Experiment 1 and 2 are shown in Table 4 and the results of the T-test are shown in Table 5 and 6. Referring to Table 4, Experiment 1 has revealed similarities in results between the DES and combined DES/ABS models. The test results in Table 5 show that the p-values for each performance measure are higher than the chosen level of significant value (0.05). Thus the Ho1_1, Ho1_2, Ho1_3, and Ho1_4, n/a 42.18 15 17 10.15 11.83 behaviour that is modelled in the combined DES/ABS model. Such behaviour (travellers searching for shortest queue while queuing) is frequent in the system under study and has affected the travellers’ wish to be served more quickly; therefore no queue is longer than another. The statistical test (Table 6) has confirmed these three performance measures (customer waiting time, number of requests to work faster and number of 9 Submitted to Elsevier Science travellers searching for the shortest queue while queuing) have shown lower p-values than the chosen level of significant value (0.05). Therefore, the Ho 2_1, Ho2_5 and Ho2_7 hypotheses are rejected. In addition, the statistical test has confirmed that there are no significant differences in both simulation models’ results between counter staff utilisation, number of travellers served, number of travellers not served, number of travellers searching for shortest queue upon arrival and number of travellers moved to the office, as their p-values are higher than the level of significant value. The Ho2 _2, Ho2_3, Ho2_4, Ho2_6 and Ho2_8 hypotheses are therefore failed to be rejected. As an overall result, modelling human combined-proactive behaviour for both DES and combined DES/ABS models is statistically different in their simulation results performance. Therefore, the Ho2 hypothesis is rejected. Table 5 : Results of T-test in Experiment 1 Performance Measures Travellers waiting time Counter staff utilisation Number of travellers served Number of travellers not served DES vs. Combined DES/ABS P-value Result P = 0.801 Fail to reject P = 0.422 Fail to reject P = 0.763 P = 0.851 Fail to reject Number of travellers searching for shortest queue (while queuing) Number of travellers moved to the office Fail to reject Fail to reject Table 6: Results of T-test in Experiment 2 Travellers waiting times Counter staff utilisation Number of travellers served Number of travellers not served Number of requests to work faster Number of travellers searching for shortest queue (upon arriving) P = 0.572 Modelling various proactive behaviours in the airport check-in services has proved that the behaviour of travellers who always seek faster service is the main reason that has influenced the performance of both simulation models. However, this is more noticeable in combined DES/ABS as modelling travellers’ behaviours is more realistic than in the DES model. The performance of the combined DES/ABS model in modelling realistic human behaviours has a significant impact on the simulation study. From the comparison investigation, new knowledge is obtained. The investigation has proven that DES is capable of producing similar results to those of combined DES/ABS when modelling the reactive human behaviour, but further complex proactive modelling produced different results. Modelling detail human behaviours in combined DES/ABS has demonstrated that modelling such behaviours produce significance impact on the simulation output performance. This study has shown that it is useful to model human proactive behaviour as detail as possible in the service industry in order to get a good understanding on the service-oriented systems performance. The best choice of simulation technique is combined DES/ABS. 6 Performance Measures Statistical test is not available DES vs. Combined DES/ABS P-value Result P = 0.000 Reject P = 0.486 Fail to reject P = 0.612 Fail to reject P = 0.218 Fail to reject P = 0.000 Reject P = 0.766 Fail to reject Conclusions and Future Work In this paper we have demonstrated the application of simulation to study the impact of human reactive and proactive behaviour service systems. In particular we were interested in finding out more about the benefits of implementing only reactive or mixed reactive and proactive behaviours. More precisely, our investigations have focused on answering the question: Is it useful to model human proactive behaviour in service industry and which simulation techniques is the best choice for modelling such behaviour? Previously, we have dealt with the reactive behaviour modelling (Majid et al, 2009) and mixed reactive proactive behaviour modelling (Majid et al, 2010) in a first case study based in the retail sector and a second case study based in the public service sector (Majid et al, 2012). We found that modelling 10 Submitted to Elsevier Science realistic proactive behaviours that habitually occur in the real system are worth modelling in the modelled situations as it has demonstrated a big impact to the overall system performance in DES and combined DES/ABS models. In this paper, we have focused on modelling different level of proactive behaviour for check-in services in the airport. Modelling the service-oriented system as realistically (proactive behaviour) as possible is found important because modelling such detail has a significant impact on the overall system performance – reducing customer waiting time and number of customers not served. We found combined DES/ABS model is suitable for modelling the levels of proactive behaviour investigated in this case study. In the future we would like to involve with more complex service-oriented systems, to test if we can generalise our findings regarding the comparison of modelling different level of proactive behaviours in DES and combined DES/ABS techniques. 8. 9. 10. 11. 12. References 1. 2. 3. 4. 5. 6. 7. Baysan, S., et al. (2009). Modeling People Flow:A Real Life Case Study in ITU Science Center. Brailsford, S. C., et al. (2006). Incorporating Human Behaviour in Healthcare Simulation Models. In Proceeding of the 38th Winter simulation Conference, Monterey, California. Kelton, W. D., et al. (2007). Simulation with ARENA. New York, USA., McGraw-Hill. Korhonen, T., et al. (2008). FDS+Evac: An Agent Based Fire Evacuation Model Pedestrian and Evacuation Dynamics 2008 Springer Berlin Heidelberg. Korhonen, T., et al. (2008). FDS+Evac: Modelling Social Interactions in Fire Evacuation. 7th Intl. Conf. on PerformanceBased Codes and Fire Safety Design Methods. Nehme, C., et al. (2008). Using DiscreteEvent Simulation to Model Situational Awareness of Unmanned-Vehicle Operators. Virginia Modeling, Analysis and Simulation Center Capstone Conference. Norfolk, VA. Majid, M. A., et al. (2009). Comparing Simulation Output Accuracy of Discrete Event and Agent Based Models: A Quantitative Approach, Summer Comnputer Simulation Conference (SCSC 2009), Istanbul, Turkey. 13. 14. 15. 16. 17. 18. Majid, M. A., et al. (2010). Modelling Reactive and Proactive Behaviour in Simulation Operational Research Society 5th Simulation Workshop (SW10). Worcestershire, England. Majid, M. A. et al.(2012).Modelling Reactive and Proactive Behaviour in Simulation: A Case Study in a University Organisation. The International Conference on Modeling and Simulation 2012 (MAS 2012) November 28-30. 2012 ,Jeju, Korea Pew, R. W. and A. S. 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In: Proceedings of the Winter Simulation Conference, pp 22122220, 9-12 December, Washington DC, USA. Siebers P.O., Aickelin U., Celia H. and Clegg C. (2010) “Towards the development of a simulator for investigating the impact of people management practices on retail performance”. Journal of Simulation, Vol 5(4). pp. 247-265. Siebers P.O. and Wilkinson I.(2011) “A First Approach on Modelling Staff Proactiveness in Retail Simulation Models”. Journal of Artificial Societies and Social Simulation, Vol 14 (2). pp. 1-25 11 Submitted to Elsevier Science Authors Biographies MAZLINA ABDUL MAJID is a Senior Lecturer in the Faculty of Computer Systems and Software Engineering, Universiti Malaysia Pahang (UMP), Malaysia. Her research interest is in discrete event simulation and agent based simulation. Her email is <mazlina@ump.edu.my>. UWE AICKELIN is a Professor in the School of Computer Science, University of Nottingham, UK. His research interests include agent based simulation, heuristics optimisation, artificial immune system. His email is <uxa@cs.nott.ac.uk>. PEER–OLAF SIEBERS is a Lecturer in the School of Computer Science, University of Nottingham, UK. The central theme in his work is the development of human behaviour models which can be used to better represent people and their behaviours in Operational Research type simulation models. His email is <pos@cs.nott.ac.uk>. .