Unit iii(part b - architectural design)

These slides are designed to accompany Software Engineering: A Practitioner’s Approach, 7/e
(McGraw-Hill, 2009). Slides copyright 2009 by Roger Pressman. 1
Chapter 9
 Architectural Design
Slide Set to accompany
Software Engineering: A Practitioner’s Approach, 7/e
by Roger S. Pressman
Slides copyright © 1996, 2001, 2005, 2009 by Roger S. Pressman
For non-profit educational use only
May be reproduced ONLY for student use at the university level when used in conjunction
with Software Engineering: A Practitioner's Approach, 7/e. Any other reproduction or use is
prohibited without the express written permission of the author.
All copyright information MUST appear if these slides are posted on a website for student
use.

Why Architecture?
The architecture is not the operational software. Rather,The architecture is not the operational software. Rather,
it is a representation that enables a software engineerit is a representation that enables a software engineer
to:to:
(1)(1) analyze the effectiveness of the design in meeting itsin meeting its
stated requirements,stated requirements,
(2)(2) consider architectural alternatives at a stage whenat a stage when
making design changes is still relatively easy, andmaking design changes is still relatively easy, and
(3)(3) reduce the risks associated with the construction ofassociated with the construction of
the software.the software.

Why is Architecture Important?
 Representations of software architecture are an enabler
for communication between all parties (stakeholders)
interested in the development of a computer-based
system.
 The architecture highlights early design decisions that
will have a profound impact on all software engineering
work that follows and, as important, on the ultimate
success of the system as an operational entity.
 Architecture “constitutes a relatively small, intellectually
graspable mode of how the system is structured and
how its components work together” [BAS03].

Architectural Descriptions
 The IEEE Computer Society has proposed IEEE-Std-
1471-2000, Recommended Practice for Architectural
Description of Software-Intensive System, [IEE00]
 to establish a conceptual framework and vocabulary for use
during the design of software architecture,
 to provide detailed guidelines for representing an architectural
description, and
 to encourage sound architectural design practices.
 The IEEE Standard defines an architectural description (AD)
as a “a collection of products to document an architecture.”
 The description itself is represented using multiple views, where
each view is “a representation of a whole system from the
perspective of a related set of [stakeholder] concerns.”

Architectural Genres
 Genre implies a specific category within the
overall software domain.
 Within each category, you encounter a number
of subcategories.
 For example, within the genre of buildings, you
would encounter the following general styles:
houses, condos, apartment buildings, office
buildings, industrial building, warehouses, and so
on.
 Within each general style, more specific styles might
apply. Each style would have a structure that can be
described using a set of predictable patterns.

Architectural Styles
 Data-centered architectures
 Data flow architectures
 Call and return architectures
 Object-oriented architectures
 Layered architectures
Each style describes a system category that encompasses: (1) aEach style describes a system category that encompasses: (1) a
set of components (e.g., a database, computational modules)(e.g., a database, computational modules)
that perform a function required by a system, (2) athat perform a function required by a system, (2) a set of
connectors that enable “communication, coordination andthat enable “communication, coordination and
cooperation” among components, (3)cooperation” among components, (3) constraints that definethat define
how components can be integrated to form the system, andhow components can be integrated to form the system, and
(4)(4) semantic models that enable a designer to understand thethat enable a designer to understand the
overall properties of a system by analyzing the knownoverall properties of a system by analyzing the known
properties of its constituent parts.properties of its constituent parts.

Data-Centered Architecture

Data Flow Architecture

Call and Return Architecture

Layered Architecture

Architectural Patterns
 Concurrency—applications must handle multiple tasks in a
manner that simulates parallelism
 operating system process management pattern
 task scheduler pattern
 Persistence—Data persists if it survives past the execution of
the process that created it. Two patterns are common:
 a database management system pattern that applies the storage
and retrieval capability of a DBMS to the application architecture
 an application level persistence pattern that builds persistence
features into the application architecture
 Distribution— the manner in which systems or components
within systems communicate with one another in a distributed
environment
 A broker acts as a ‘middle-man’ between the client component and
a server component.

Architectural Design
 The software must be placed into context
 the design should define the external entities (other
systems, devices, people) that the software interacts
with and the nature of the interaction
 A set of architectural archetypes should be
identified
 An archetype is an abstraction (similar to a class)
that represents one element of system behavior
 The designer specifies the structure of the
system by defining and refining software
components that implement each archetype

Architectural Context
target system:
SecurityFunction
uses
uses peershomeowner
Safehome
Product
Internet-based
system
surveillance
function
sensors
control
panel
sensors
uses

Archetypes
Figure 10.7 UML relationships for SafeHomesecurity function archetypes
(adapted from [BOS00])
Controller
Node
communicates with
Detector Indicator

Component Structure
SafeHome
Executive
Ext ernal
Communicat ion
Management
GUI Internet
Interface
Funct ion
selection
Security Surveillance Home
management
Control
panel
processing
detector
management
alarm
processing

Refined Component Structure
sensorsensor
sensor
sensor
sensor
sensorsensor
sensor
External
Communication
Management
GUI Internet
Interface
Security
Cont rol
panel
processing
det ect or
managem ent
alarm
processing
Keypad
processing
CP display
funct ions
scheduler
sensor
sensor
sensor
sensor
phone
com m unicat ion
alarm
SafeHome
Executive

Analyzing Architectural Design
1. Collect scenarios.1. Collect scenarios.
2. Elicit requirements, constraints, and environment description.2. Elicit requirements, constraints, and environment description.
3. Describe the architectural styles/patterns that have been3. Describe the architectural styles/patterns that have been
chosen to address the scenarios and requirements:chosen to address the scenarios and requirements:
•• module viewmodule view
•• process viewprocess view
•• data flow viewdata flow view
4. Evaluate quality attributes by considered each attribute in4. Evaluate quality attributes by considered each attribute in
isolation.isolation.
5. Identify the sensitivity of quality attributes to various5. Identify the sensitivity of quality attributes to various
architectural attributes for a specific architectural style.architectural attributes for a specific architectural style.
6. Critique candidate architectures (developed in step 3) using the6. Critique candidate architectures (developed in step 3) using the
sensitivity analysis conducted in step 5.sensitivity analysis conducted in step 5.

Architectural Complexity
 the overall complexity of a proposed
architecture is assessed by considering the
dependencies between components within the
architecture [Zha98]
 Sharing dependencies represent dependence
relationships among consumers who use the same
resource or producers who produce for the same
consumers.
 Flow dependencies represent dependence relationships
between producers and consumers of resources.
 Constrained dependencies represent constraints on the
relative flow of control among a set of activities.

ADL
 Architectural description language (ADL) provides
a semantics and syntax for describing a software
architecture
 Provide the designer with the ability to:
 decompose architectural components
 compose individual components into larger architectural
blocks and
 represent interfaces (connection mechanisms) between
components.

An Architectural Design Method
"four bedrooms, three baths,
lots of glass ..."
customer requirements
architectural design

Deriving Program Architecture
ProgramProgram
ArchitectureArchitecture

Partitioning the Architecture
 “horizontal” and “vertical” partitioning are
required

Horizontal Partitioning
 define separate branches of the module
hierarchy for each major function
 use control modules to coordinate
communication between functions
function 1function 1 function 3function 3
function 2function 2

Vertical Partitioning: Factoring
 design so that decision making and work
are stratified
 decision making modules should reside at
the top of the architecture
workers
decision-makers

Why Partitioned Architecture?
 results in software that is easier to test
 leads to software that is easier to maintain
 results in propagation of fewer side effects
 results in software that is easier to extend

Structured Design
 objective: to derive a program
architecture that is partitioned
 approach:
 a DFD is mapped into a program
architecture
 the PSPEC and STD are used to
indicate the content of each module
 notation: structure chart

Flow Characteristics
Transform flow
Transaction
flow
This edition of
SEPA does not
cover transaction
mapping. For a
detailed
discussion see the
SEPA website

General Mapping Approach
isolate incoming and outgoing flowisolate incoming and outgoing flow
boundaries; for transaction flows, isolateboundaries; for transaction flows, isolate
the transaction centerthe transaction center
working from the boundary outward, mapworking from the boundary outward, map
DFD transforms into corresponding modulesDFD transforms into corresponding modules
add control modules as requiredadd control modules as required
refine the resultant program structurerefine the resultant program structure
using effective modularity conceptsusing effective modularity concepts

General Mapping Approach
 Isolate the transform center by specifying incoming
and outgoing flow boundaries
 Perform "first-level factoring.”
 The program architecture derived using this mapping
results in a top-down distribution of control.
 Factoring leads to a program structure in which top-level
components perform decision-making and low-level
components perform most input, computation, and output
work.
 Middle-level components perform some control and do
moderate amounts of work.
 Perform "second-level factoring."

Transform Mapping
data flow model
"Transform" mapping
a
b
c
d e f
g h
i
j
x1
x2 x3 x4
b c
a
d e f g i
h j

Factoring
typical "worker" modules
typical "decision
making" modules
direction of increasing
decision making
Architectural

First Level Factoring
main
program
controller
input
controller
processing
controller
output
controller

Second Level Mapping
D
C
B
A
A
C
B
Dmapping from the
flow boundary outward
main
control

Unit iii(part b - architectural design)

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