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Developing a Repeating Model Using the Structured Spreadsheet - - PowerPoint PPT Presentation

Developing a Repeating Model Using the Structured Spreadsheet Modelling and Implementation Methodology EuSpRIG 16th Annual Conference, 2015London, UK Paul Mireault Founder, SSMI International Honorary Professor, HEC Montral


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Developing a Repeating Model Using the Structured Spreadsheet Modelling and Implementation Methodology

EuSpRIG 16th Annual Conference, 2015—London, UK Paul Mireault Founder, SSMI International Honorary Professor, HEC Montréal Paul.Mireault@SSMI.International

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Presentation Plan

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  • Genesis
  • SSMI
  • Repeating Sub-model
  • Structured Implementation
  • Characteristics of the SSMI Methodology
  • Q&A
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Genesis

  • Teaching Decision Support Systems courses (1980’s and

1990’s)

  • Undergraduates
  • MBAs
  • Reference book: Modern Decision Making, Samuel Bodily,

1985

  • Implement models using IFPS
  • Gradually adapted to Lotus 1-2-3 and Excel

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Genesis

  • Teaching the core IS course (HEC Montréal)
  • MBA students
  • Undergraduate students
  • Executives

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Instead of teaching Excel, I teach how to use Excel.

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Physical Model Time Disk Excel manipulations User Computer Logical and mechanical errors

Typical Process

Spreadsheet Analysis, Design and Implementation

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Typical Process

Spreadsheet Analysis, Design and Implementation

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Source: Hermans, Felienne (2014): Enron Spreadsheets and Emails. figshare. http://dx.doi.org/10.6084/m9.figshare.1221767

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Model or Model?

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Model or Model?

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It can be an 
 accounting system; Used for simulation and forecasting; Or presented as a dashboard.

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Model or Model?

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A spreadsheet is a model of the real world The Formula Diagram and the Formula List are the Conceptual Model of the spreadsheet

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Model or Model?

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Formula Diagram Formula List

In Information Systems, we use a Conceptual Model.

  • Describes what the user needs, without references to the

technology used to implement it.

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Structured Spreadsheet Modelling and Implementation

Disk

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Disk Excel manipulations Spread- sheet file Developer Computer Domain knowledge Spreadsheet knowledge Formula Diagram and Formula List Same or another developer Mechanical errors Conceptual and Logical Models Physical Model Time Logical errors

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Structured Modelling

Behind-the-Scene Interface Constants Calculated

Input Calculated Variable Output

Two categories of variables, with sub-categories:

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Example

  • Marco sells widgets in three regions:
  • {East, South and North}
  • Past demand = {48%, 23%, 29%}
  • Delivery Cost = {50$, 80$, 60$}
  • Unit manufacturing cost = 120$
  • Demand = 367000 × 1.009−Price

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South Region

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Other Regions

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What if…

  • 10 provinces?
  • 50 states?
  • 100 departments?

How big?

Other Regions

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Repeating Sub-Model

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Structured Implementation

  • Three-tier architecture: single-purpose worksheets
  • Parameters
  • Model
  • Interface
  • Emulate SE Modules with precise block structure
  • Extensive use of names

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Worksheet for

Single-Value Parameters

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Every cell is named

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Worksheet for

Multiple-Value Parameters

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Every row is named

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Worksheet for

Single-Value Calculated Variables

The definition block:

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Simple 
 reference formulas to named variables Definition formula referencing the cells 
 directly above Every cell containing a definition formula is named

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Worksheet for

Multiple-Value Calculated Variables

The definition block:

Simple 
 reference formulas to named variables Definition formula referencing the cells 
 directly above Every row containing a definition formula is named

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Worksheet for

Multiple-Value Calculated Variables

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Worksheet for

Multiple-Value Calculated Variables

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Calculating a

Single-Value Variable from a Multiple-Value Variable

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Calculating a

Single-Value Variable from a Multiple-Value Variable

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Interface Flexibility

Original Version SSMI Version

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Interface Flexibility

SSMI Version

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Behind-the-Scenes

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Characteristics of the SSMI Methodology

  • Spreadsheet documentation: Formula Diagram and

Formula List

  • Overview of relationships
  • Facilitates peer review
  • Facilitates hand-off of the model

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Characteristics of the SSMI Methodology

  • Rule 1: only one mathematical operator or function

per formula

  • References in the definition block are made by name
  • Easier to understand their meaning
  • The definition formula uses the cells directly above,

making it easier to verify.

  • There is never any need to use absolute or mixed cell

references

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Characteristics of the SSMI Methodology

  • No daisy-chains
  • Instead of copying many formulas one by one, we copy

all the formulas once

  • Verifying an implementation can be done by re-copying

column B and seeing where changes happen

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In Development

  • Repeating sub-model with time periods.
  • Modelling techniques for special cases.

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Q&A

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Thank you!

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