Shopping Network


ExSpect course exercise

February 1996

March 10, 1996 Márton Fernezelyi

Course description: (English - Hungarian)

Course on Business modelling, supported by automated tools, by dr. R.J.C. Kusters, dr. Marc Voorhoeve, dr. Lou Somers and Ron Vodegel, Eindhoven University of Technology, 22 January - 3 February 1996

Original documentetion:

WinWord format exspect.doc
RTF format exspect.rtf

Source code:

ExSpect file assignment.ex

Main idea:

We have to simulate a shopping network. The system based on a distribution center with three shops each with one customer and a supplier connected to the distribution center. We have to build up a monitoring system to check the average level of the stocks.

The top model:

Description of the basic element:


Every customer has the same behavior. They send one order in every 2 seconds to the shops with random selection from the available goods. The customer accepts all the arriving articles. As only one customer connected to each shop in my system special identifier not needed.


In my network I build up three shops. Every shop has a unique ID to make difference between the orders sent to the distribution center. In the model every shop has two independent stores. First is the real store with the amount of goods available. Second is the virtual store with the ordered stock level. At the beginning the starting stock levels in the two stores are the same. The shop accepts every order. If there is not enough article in the real store the order has to wait for the service. If the stock level is too low in the virtual stock the shop sends an order to the distribution center. If the stock is available the warehouse delivers immediately, if not it is necessary to wait for the delivering from the supplier.

Distribution center:

The distribution center and the shops have manly the same functionality. While the supplier delays with the delivery some time 7 days the distribution center has higher stock level then the shops.


The supplier receives orders from the warehouse, and satisfies it with a random delay between 2 and 7 days. The delay's distribution over this interval is uniform.

Monitoring system:

The monitoring system collects information from the shops and the distribution center. Every time when the real stock has changed the monitoring system receives the old stock levels from the shops and the distribution center. The monitoring system calculates the average stock level at every change.

Simulation results after four weeks:

Shop 1
Average Stock Level
Article type
avg: real: 50.1167prodid: str: bike
avg: real: 52.2719prodid: str: radio
avg: real: 53.3104prodid: str: tv
avg: real: 54.2570prodid: str: moto

Shop 2
Average Stock Level
Article type
avg: real: 48.7071prodid: str: tv
avg: real: 52.2374prodid: str: radio
avg: real: 53.4782prodid: str: bike
avg: real: 53.8712prodid: str: moto

Shop 3
Average Stock Level
Article type
avg: real: 47.8609prodid: str: moto
avg: real: 49.7075prodid: str: radio
avg: real: 50.6471prodid: str: tv
avg: real: 53.3478prodid: str: bike

Distribution center
Average Stock Level
Article type
avg: real: 83.2323prodid: str: moto
avg: real: 84.9410prodid: str: tv
avg: real: 87.3464prodid: str: radio
avg: real: 97.7654prodid: str: bike

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Last modified: March 12, 1996,