for ITU SMDF2009

1. System Choice
Overview, Principles and Techniques
Chapter 2
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The System’s Context
System
User
Problem domain Application domain
The purpose of system choice is to define the
context of the system
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Activities
Re quirements
Pro blem-
Application-
for use
do main
dom ain
ana lysis
analysis
Situation Ideas Create foundation and
For system design
And interpretations criterion of relevance
Component
for Model
design
Speci fications of
compo nents
Systems System definition
Specifications of
archite cture
Architectural
design
System definition:
a concise description of a
computerized system expressed
in natural language
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Side 1

2. Result (example)
Systemdefinition:
A computerized system used to prepare and plan an IFIP
conference, with emphasis on administration of participants,
articles, and the program itself.
The system should primarily be an administrative tool, but
secondarily serve as a communication medium for the program
committee, the organizing committee, and the local administrative
personnel to help them manage the conference.
The system should be based on a cheap PC with current tools.
The system should also be able to function in different types of
environments, including use by volunteers who have great
enthusiasm and greatly variable administrative experience.
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Describe the Situation Principle: Appreciate the situation
(using Rich Pictures)
#1
• Expresses different views Tradition vs.
change
• Focus:
– on change or stability Individual info.
#2
• Processes such as:
– work, production, information
processing, exchange, #3
Pool
planning, control, development,
Standard inf o.
organizational change
Reorganizing
• Structures such as: #4
– production, use, application, Resources
Personnel info.
communication, deal,
ownership, membership, #5
relationship, power
• Rich pictures
– but not chaotic Plans
#6
Coordinating
New entity
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Ideas for symbols for Rich Pictures
ABC… 123…
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Side 2

3. Rich Picture (example) with Focus on
Stability
reception of
calls
d isp atcher
custome rs
ta sks
Where is it?
When a re
they re ad y?
5 0 cars
h osp ital
emergency vehicle
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Create Ideas
• Exemplars (e.g. for a • Experiments with
financial system): prototypes:
– Study an existing system – Planning
– Look at spreadsheets – Development
– Examine standard packages – Preparation
– Consider SAP – Test
– Summarizing
• Metaphors (e.g. for a
library):
– Storage
– Supermarket
– School
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Different kinds of prototyping
• exploratory prototyping:
– to clarify requirements
– to discuss different solutions
• experimental prototyping
– determining the adequacy of a proposed solution
• evolutionary prototyping
– adapting the system to possibly changing
requirements
© Christiane Floyd
© Christiane Floyd
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Side 3

4. Systems are holistic views
• A system definition expresses a
perspective on something The Earth seen from
Apollo 17.
From a holistic
• Every system definition represents a perspective, the
universe exists in and
specific perception of the real world forms integrated webs
of wholeness, often
beyond our direct
filtered through the ideas, conceptions, perception (Wikipedia)
educations and backgrounds of the
people involved
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System Definition (FACTOR)
Functionality: The system functions that support the application-domain
tasks.
Application domain: Those parts of an organization that administrate,
monitor, or control a problem domain.
Conditions: The conditions under which the system will be developed and
used.
Technology: Both the technology used to develop the system and the
technology on which the system will run.
Objects: The main objects in the problem domain.
Responsibility: The system’s overall responsibility in relation to its context.
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Hair Salon
F Support for work planning
A system for use in a hair salon in the daily
(schedules) and appointments.
work of managing customers and
appointments, as well as earlier treatments of A Managing customers, their
regular customers. treatments, and appointments, and
planning employees’ work
The system should also be used by the salon
schedules.
owner for planning employees’ work schedules.
Appointments are integrated to help arrange C Development in close collaboration
work schedules. with employees.
The system should be a reliable and fast tool in T Smaller PC or Macintosh with large
the daily work and should also be a common graphical screen.
medium for work schedules (appointments).
O Customers, employees,
The system is based on a single, small (and appointments, and work schedules..
cheap) PC or Macintosh with a large graphical
R Tool for reliable administration and
screen (17”), capable of showing detailed work
a common mediator in the salon.
schedules.
The development process should be conducted
in close cooperation with the salon employees.
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Side 4

5. Define Systems and Alternatives
• Responsibility 1
• Functionality 1
– Support program design by
– Register information about
producing overviews and
participants and produce a
allowing users to add
complete participant list.
components and save different
• Functionality 2
versions. Support conference
– Register general participants as operations by emphasizing
well as those with an active role potential problems at regular
such as author, speaker, or intervals.
reviewer. Support the
• Responsibility 2
administration of finances and
– Automatic conference-planning
invitations. Support
program. Generate program
development of conference
from suggested sessions and
programs, including
incoming paper reviews.
registration, paper acceptance,
and sessions divisions.
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Evaluation and Choice
• Do this as early as possible
• Iterate within the activity and in subsequent
activities
• The purpose is to choose one system
• It is the choice of the customer
• System developers provide support and
organize the process
• Approach: question overall decisions and
evaluate alternatives
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System Choice: Summary
• To agree on the overall system characteristics.
Purpose
• System definition: A concise description of a
Concept computerized system expressed in natural
language.
• Appreciate the situation.
Principles • Cultivate new ideas.
• Define alternative systems.
• A system definition that fulfills the FACTOR
Results criterion.
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Side 5

6. Task for the rest of today and until the
next OOA&D exercise
• Meet in groups and identify a simple system case
you can use for your project
• Start to work on the system definition!
1. Describe the situation in your case by one or more rich
pictures.
1. Create one each, and compare and explain
2. Generate ideas for computerized functions.
3. Make a system definition.
4. Formulate alternatives by varying one or more elements in
the system definition (could be different opinions about the
characteristics of the system).
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Examples of cases
Find your own case - or use the
• Video rental (Ex. 13, ch 3)
• Mobile Phone (Ex. 14, ch 3)
• Teaching Administration (Ex. 15, ch 3)
• Elevator Control (Ex. 16, ch 3)
.... the idea is to try out the techniques!
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References
• L. Mathiassen et al. Object Oriented Analysis and Design. 2000,
chapter 16.
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Side 6