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DSS News
D. J. Power, Editor
April 8, 2007 -- Vol. 8, No. 7
A Free Bi-Weekly Publication of DSSResources.COM
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Featured:
* Ask Dan: What are the features of a model-driven DSS?
* DSS Conferences
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Ask Dan!
What are the features of a model-driven DSS?
by Dan Power
Editor, DSSResources.com
This is the final column about features of computerized decision
support systems. The focus is on model-driven decision support
systems. The goal remains to identify from a user's perspective
major, observable aspects, attributes or elements that distinguish
one type of DSS from other types of DSS (Power, 2002) and from other
computerized information systems.
In general, a model-driven DSS provides access to and manipulation of
a quantitative model. DSS built using simple algebraic models provide
the most elementary level of functionality. In general, model-driven
DSS use more complex models, e.g., accounting, optimization and
simulation, to provide decision support. In most implementations,
model-driven DSS use the data and parameters provided by a decision
maker to help in analyzing a situation. Model-driven DSS do not
usually require large historical databases. Early versions of
model-driven DSS were called model-oriented DSS by Alter (1980) and
computationally-oriented DSS by Bonczek, Holsapple and Whinston
(1981).
Alter (1980) identified DSS built using accounting models,
representational models and optimization systems. These three
subtypes of model-driven DSS have many shared features, but because
of differences in the underlying modeling technology additional or
modified features associated with manipulating the specific model are
sometimes provided. To add to the complexity, a specific model-driven
DSS may also have multiple subsystems that use various models. In
general, the initial model-driven DSS built in the 1970s were largely
independent of centralized information systems (cf., Keen, 1981) so
users had to supply all of the data used by the system. Today's
model-driven DSS are more likely to be integrated with other DSS and
Information Systems.
Accounting models use accounting definitions to calculate the
consequences of planned actions. A DSS that helps prepare monthly or
quarterly budget forecasts probably uses an accounting model.
Accounting models assume certainty in a situation about input
parameters.
Representational models try to capture the dynamic behavior of a
system and estimate the consequences of actions where there is
uncertainty. Simulation is the most commonly used process for
studying dynamic systems. For example, a store manager may use
simulation in a DSS with an inventory model to determine order
quantities. Also, simulation is often used in one time special
decision support studies.
Optimization systems help estimate the results for various decision
alternatives given a set of constraints. Linear programming is the
most widely used optimization technique. A typical DSS application of
linear programming involves resource allocation. For example, a DSS
with optimization might assist a saw mill operator in determining how
to cut a log to minimize waste or help a production manager blend
inputs to minimize costs and still meet product constraints.
Optimization is also used in one time special decision support
studies.
Model-driven DSS are used to assist in formulating alternatives,
analyzing impacts of alternatives, and interpreting and selecting
appropriate options. Tasks that have been supported with model-driven
DSS include crew deployment, job scheduling, advertising allocation,
forecasting product usage, cost estimation and pricing, tax planning
and investment analysis.
A classic example of model-driven DSS is the system implemented at
Gotaas-Larsen Shipping Corp. in the late 1970s (cf., Alter, 1980).
The company used a DSS for preparing and revising a 15 month
operation plan for its cargo ships. The model-driven subsystem
supported cash flow and pro forma analyses on a per ship, per voyage,
per division and company-wide basis. The DSS helped users simulate
results. The computerized system aggregated plans for individual
feasible voyages to help managers assess whether the overall plan
would be effective. A data-driven subsystem provided variance reports
and performance tracking.
Concannon and Tudor (1992) reported development of a visual
interactive model-driven DSS that was used to support railroad track
maintenance operations. The DSS helped monitor and prioritize track
maintenance work including scheduling repair crews. The goal was to
schedule track maintenance in a cost-effective manner with minimal
disruption to commercial traffic. A data-driven subsystem helped
managers compare actual maintenance performance to the plan.
Computerized quantitative models are often developed as part of a
decision support special study and these applications are sometimes
incorrectly identified as DSS. In most cases in a special study, the
application user interface in not as sophisticated and feature laden
as is one found in a DSS. Examples of one time special studies that
use models include merger and acquisition analysis, lease versus
purchase decisions, new venture analysis, capital budgeting, and
equipment replacement decisions. Turban and Aronson (1998) explain
how Siemens' Solar Industries used a computer simulation built using
ProModel to evaluate alternative designs for a photocell fabrication
"cleanroom" (p. 146) and Wesleyan University's development of a
student aid planning model (p. 292). Both Siemen's Solar Industries
and Wesleyan University used the results of a decision support
special study that relied upon quantitative models, but neither
organization built and used a model-driven DSS. When classifying
computer applications, the criteria in Power (2004) can help avoid
classifying model-based special studies with model-driven DSS.
The following are major features of model-driven DSS from a user's
perspective:
1) Change a model parameter or classic "what if" analysis. Performing
"what if" analysis involves varying a single model input parameter
over a reasonable range. This is a major feature of model-driven DSS.
For example, a slider may be used to adjust values in a range.
2) Context specific help and model definitions. Users of a
model-driven DSS often have questions about the quantitative model,
its assumptions and the relationships among variable. A good
model-driven DSS provides online help. The system may include a
graphical representation of the model.
3) Create and manage scenarios. A scenario is a specified combination
of values assigned to one or more variable cells in a model. In Excel,
scenarios can involve as many as 32 variables. The scenario summary
examines relationships between scenarios. Some model-driven DSS have
predefined scenarios while other systems make it easy for users to
add and modify scenarios.
4) Extract specific historical data values from an external database.
For example, a model-driven DSS for investment analysis may provide a
capability to extract historical stock information.
5) Generate a sensitivity analysis. Users often want to determine the
impact of systematic changes in the values of one or two variables
over a reasonable range on the results of a model. This capability is
called sensitivity analysis (see Power, 2006). In Excel, one and two
variable data tables can provide sensitivity analysis. In a
model-driven DSS, the sensitivity analyses are usually predefined and
in addition to data tables, charts are often provided to visually
display the sensitivity of results.
6) Output selection. Model-driven DSS usually have multiple formats
for displaying outputs. For example, it may be possible to select a
pie or a bar chart. Some DSS based upon simulation provide a visual
animation as the process simulation is occurring.
7) Specify and seek goals. Goal seek is a capability for specifying
the desired result of a model. In Excel, when using goal seek the
value in a specific cell is varied until the formula that is
dependent on that cell returns the desired result.
8) Store inputs, results and user actions.
9) Value elicitation and data input. Values are elicited from the
user of a model-driven DSS (Power, 2003b). There are three primary
approaches for eliciting values: 1) numerical, 2) graphical, and 3)
verbal.
The benefits of model-driven DSS include: 1) examining more
alternatives; 2) gaining insights about how a process works; 3)
making better and more effective decisions; 4) reducing clerical
work; and 5) reducing costs and saving time, especially reduction in
decision process cycle time.
Please note: A quantitative model is an abstraction of relationships
in a complex situation and the results of using a specific
model-driven DSS need to be carefully monitored for ongoing validity
and usefulness. If the model is incomplete, inaccurate or
misspecified, the results can actually negatively influence a
decision makers judgment. Model-driven DSS should be periodically
reviewed and when necessary revised.
As always your comments, questions and suggestions are welcomed.
References
Alter, S.L. Decision Support Systems: Current Practice and Continuing
Challenge. Reading, MA: Addison-Wesley, 1980.
Bonczek, R. H., C.W. Holsapple, and A.B. Whinston. Foundations of
Decision Support Systems, New York: Academic Press, 1981.
Concannon, K and S. Tudor, "Visual Interactive DSS Streamline
Maintenance Operations," OR/MS Today, Dec. 1992.
Keen, P.G.W., "Value analysis: Justifying decision support systems,"
MIS Quarterly, 5:1, 1981, 1-16.
Mallach, E.G., Understanding Decision Support Systems and Expert
Systems, Burr Ridge, IL, Irwin, 1994.
Power, D. J., Decision Support Systems: Concepts and Resources for
Managers, Westport, CT: Greenwood/Quorum, 2002.
Power, D., How can simulation be used for decision support? DSS News,
Vol. 4, No. 14, July 6, 2003 (a).
Power, D., What DSS interface design is "best" for eliciting values?
DSS News, Vol. 4, No. 11, May 25, 2003 (b).
Power, D., What type of DSS is X? or What type of DSS is a revenue
management application? DSS News, Vol. 5, No. 7, March 28, 2004.
Power, D. J., "How does sensitivity analysis differ from 'What If?'
analysis?" DSS News, Vol. 7, No. 16, July 30, 2006.
Turban, E. and J. E. Aronson, Decision Support Systems and
Intelligent Systems (5th edition), Upper Saddle River, NJ: Prentice
Hall, 1998.
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DSS Conferences
1. MySQL Users Conference, April 23-26, 2007 Santa Clara,
California. Check http://www.mysqlconf.com .
2. ISCRAM 2007, May 13-16, 2007 Delft, The Netherlands.
Check http://www.iscram.org .
3. MWAIS data warehousing workshop with Ron Swift, Friday
morning, May 18, 2007, check http://mis.uis.edu/MWAIS2007/ .
4. Crystal Ball User Conference, May 21-23, 2007 Denver.
Check http://www.crystalball.com/cbuc/index.html.
5. AMCIS 2007, Americas Conference on Information Systems,
Keystone, CO USA, August 9-12, 2007. SIG DSS mini-tracks.
Check http://www.biz.colostate.edu/amcis07/ .
6. DaWaK 2007, 9th International Conference on Data
Warehousing and Knowledge Discovery, Regensburg, Germany,
September 3-7, 2007. Full papers due: April 13, 2007.
Check http://www.dexa.org/ .
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83 frequently asked questions about computerized DSS
http://dssresources.com/dssbookstore/power2005.html
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What's New at DSSResources.COM
04/07/2007 Started a new feature at DSSResources.com and posted the
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