This document provides an overview of Ventana Systems UK Ltd, a small consultancy specializing in system dynamics modeling. It describes their services such as policy design, simulation, and training. It also discusses key concepts in system dynamics modeling like feedback loops, stocks and flows, variables, delays, and how simple models can evolve into more complex models.

1. Capabilities
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2. What we do ?
System DynamIcs
Policy System
Design Description
Simulation
Products Consultancy Training
Copyright Ventana Systems UK Ltd 2008

3. Who are we ?
• Small independent consultancy, specialising in
Vensim/System Dynamics modelling
• Our consultant team have worked together for
15 years
• Bases in
– Liverpool
– Southampton
– Salisbury
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4. Some of our clients
Leading Pharmaceutical
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5. System Dynamics
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6. System Dynamics
• A modelling methodology for addressing
complex business environments using a
holistic systems approach.
• The core of System Dynamics is the
understanding of the cause and effect
relationships within the system and to
assess the impact of change.
Copyright Ventana Systems UK Ltd 2008

7. System Dynamics
• System dynamics is an approach to
understanding the behaviour of complex
systems over time.
• It deals with internal feedback loops and time
delays that affect the behaviour of the entire
system.
• What makes using system dynamics different
from other approaches to studying complex
systems is the use of feedback loops and stocks
and flows.
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8. Stock & Flow Diagrams
Stock/Level
Inflow Outflow
External Data Auxiliary Table
Constant
• Stock and flow diagrams are the most common first step in building
a simulation model because they help define types of variables that
are important in causing behaviour.
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9. Variables Types
• Stocks – Accumulation over time
– Eg Money, information, people, inventory,
• Flows – Rate stocks change over time
– Eg Earnings, Hiring, production rate,
• Auxiliary – Formulate complex rate eqns
– Eg Desired production, Target workforce,
• Constants – Static inputs
– Eg Initial stock value, Item price, delay times
• Tables – Nonlinear relationships
– Eg Demand curves, pre defined dependent variable relationships
• External Data – Real world time series
– Eg Sales data, census data, interest rates
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10. System Delays
Time Delay
Decision Implementation Results Consequence
• Vacancy to Recruitment
– Advertise
– Shortlist
– Interview
– Selection
– Notice Period
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11. Feedback
+
Revenue
• Increased Demand
Profit +
+
 Higher Price Supply
+
-
• Higher Price +
Price
 Greater Supply Marketing -
+
Demand
• Abundant Supply
+
 Lower Price
• Lower Price
 Greater Demand
Action Consequence
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12. From Simple Models
fraction facilities ready
Orders in Orders
Requiring
Process Testing
orders processing testing
target test delay
target process delay
start orders Testing
Capacity
test adj time
Processing
Capacity
fraction facilities good
Orders
proc adj time Requiring Awaiting
Service dispatching Activation
target service delay
target activation activating
delay
Dispatching
Capacity Activating New
Capacity Customers
dispatch adj time activation adj time
Copyright Ventana Systems UK Ltd 2008