Stumpf and Teague
Object-Oriented Systems Analysis and Design with UML
.
Chapter 7
Information System Design
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Learning Objectives
• Describe how analysts and designers
view system requirements from different
perspectives.
• Explain why analysts and designers
view the boundary between analysis and
design differently than managers do.
• State some goals of information system
design.
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Learning Objectives
(continued)
• Distinguish among batch, online,
interactive, and real-time systems.
• Name and state the purpose of each of
the layers of a three-tier system
architecture.
• Give examples of each of the three
generic types of hardware components
of a computer information system.
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Learning Objectives
(continued)
• Explain the function of infrastructure
and administration components in a real
information processing system.
• Discuss what additional design
decisions and system components are
required in distributed systems.
• Describe the principal subsystems into
which a computer information system is
partitioned.
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Overview
Analysis defines users’ requirements
for a new information processing
system.
The principal goal of design is to specify
a realizable information processing
system which satisfies the
performance standards of the
requirements specification.
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Overview
(continued)
Designing the overall system structure
involves partitioning the system into
three major subsystems – the
application programs, the user
interface, and the data base.
Thereafter, these subsystems may be
treated as relatively independent
design problems.
© 2005 Prentice Hall
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Overview
(continued)
This partitioning is implemented as
a layered architecture, which is
considered to be best practice.
The hardware of an informationprocessing system consists of
three generic types of components:
channels (which transport
information), containers (which store
information), and processors (which
transform information).
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Overview
(continued)
A real information-processing system
must contain components which
compensate for the imperfections
of the hardware.
Before the end of design, the design
must be made consistent with the
decisions about the hardware and
system software environment and
with the specifics of the system
acceptance tests.
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System Design in the
Rational Unified Process
FIGURE 7.1
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The Transition from
Analysis to Design
Analyst’s Viewpoint: Analysis defines
a problem. It focuses on an essential
description of what the system must
do.
Designer’s Viewpoint: Analysis offers
clues to a solution and to tests to
determine whether a proposed
design is satisfactory.
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Technical and Management
Issues in the Transition
•
The technical criterion for exiting
analysis is: “Have all the users’
requirements been adequately
defined?”
•
The managerial criterion for exiting
analysis is: “Is the project worth
continuing?”
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Goals of Computer
Information System Design
1. Solving the problem posed in the
requirements specification
2. Satisfying the performance
requirements determined during
systems analysis
3. Deriving an automated system whose
structure fits the structure of the
problem
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Goals of Computer Information
System Design (continued)
4. Considering alternative system
designs to select the one most
suitable for the organization
5. Matching the application software
design to the hardware and system
software environment in which it will
operate
6. Creating a system whose structure
makes it easy to understand,
construct, and modify
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Characteristics of a
System Design Specification
• Explicit: spells out what is critical
• Complete: in scope and detail
• Unambiguous: only one possible
interpretation
• Consistent: no internal conflicts
• Accurate: no mistakes requiring
subsequent correction
• Minimally redundant: facilitates
changes to the design
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Batch, Interactive,
and Real-Time Systems
In a batch system the system inputs are
stored at or near the system boundary.
They are processed in batches. The
storage introduces a time delay.
In an interactive system inputs enter the
system one at a time. Time delays are
handled internally.
A real-time system responds rapidly
enough for its output to affect or
control events in its environment.
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The Three- Tier
Layered System Architecture
FIGURE 7.5
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Generic Hardware Components
• Processors: transform information
• Containers: store data
• Channels: transport information
Appropriately allocating channels,
containers, and processors to each of
the layers of the three-tier architecture
is the fundamental design problem at
the system level.
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Channels, Containers,
and Processors
FIGURE 7.6
.
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Technology of a Real
Information Processing System
In contrast to an essential system,
a real system must incorporate
additional components to
compensate for imperfections
in real-world technology.
•
•
Infrastructure provides additional
communication.
Administration provides additional
quality control and coordination.
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Distributed Systems
Distributed systems have processors or
data bases in more than one location.
They are usually organized as client/server
systems with three types of components:
• Client machine requests a service from
another machine in the system.
• Server machine carries out the request
and returns the results to the client.
• Communications network transmits
messages between client and server.
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Communications Networks
• Network types: Local, metropolitan,
wide area networks
• Network protocols: Specify formats for
messages between processes
• Network components: Routers, switches,
hubs, modems, codecs, multiplexers
• Telecommunications software: Manages
the communications in distributed
systems
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Other Components
of an Implementation
• Application software: Carries out
application-specific transformations
• System software: Manages computer
resources and supports applications
• Data base: Stores data in an organized
structure in non-volatile memory
• User interface: Enables communication
between humans and computers
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Activities of System Design
.
FIGURE 7.9
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System Acceptance Tests
The system acceptance tests measure
whether a completed system is
acceptable to its users.
They are based on the performance
requirements specified in analysis.
Ideally, the tests should be defined by
people who are not responsible for
developing the system.
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Activities of
Designing the System Structure
1. Specify the external interface.
2. Allocate essential use cases to
processors.
3. Allocate stored data to storage devices.
4. Establish the infrastructure for
communication.
5. Add the intra- and interprocessor
administration.
6. Select the best system structure.
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Alternative A –
Public University System
.
FIGURE 7.13
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Alternative B –
Public University System
.
FIGURE 7.14
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Alternative C –
Public University System
.
FIGURE 7.15
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Summary
A layered system architecture of at least
three tiers represents best practice for
information system design.
The fundamental system design problem
is to appropriately allocate processors,
containers, and channels to each layer
of this architecture.
Once the system architecture is defined,
the design may be partitioned into
program, database, and user interface
design problems.
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